Review
DOI: 10.1002/ijch.201400047
What Currently Limits Charge Carrier Mobility in Crystals
of Molecular Semiconductors?
Guillaume Schweicher,[a] Yoann Olivier,[b] Vincent Lemaur,[b] and Yves Henri Geerts*[a]
In memory of Michael Bendikov
Abstract: Charge carrier mobility is a central property that
characterizes the performances of organic semiconductors
and is mostly measured in field-effect transistors. High mobility values are sought by many research teams. This article, that provides an overview of best performing molecular
semiconductors is constructed on the question: What cur-
rently limits charge carrier mobility in crystals of molecular
semiconductors? With this in mind, we confront, in a critical
way, the current theoretical understanding to the most salient experimental results with the hope to reach a deeper understanding based on first principles and order of magnitudes of the main physical parameters.
Keywords: charge carrier mobility · charge transfer · electrochemistry · semiconductors · structureactivity relationships
1 Introduction
Organic electronics is a vivid field of research with about
3000 publications per year, among which around 1000 are
progress reports linked to organic field-effect transistors
(OFETs) and charge transport. Charge carrier mobility, m
(cm2 V1 s1), defined as the drift velocity of the charge
carrier (cm s1) per unit of applied electric field (V cm1),
occupies a pivotal role because it characterizes semiconductor ability to transport charges and it limits device
performances, notably the transistor switching rate, which
is an important parameter for electronic circuits.[1–4] The
synthesis of novel conjugated and aromatic molecular
structures is largely driven by the hope of discovering
new organic semiconductors with record charge carrier
mobility.[5–9] Even if charge carrier mobility is determined
by the molecular structure of p systems, crystal packing is
of equal importance.[10–22] Rubrene (4), one of the most
studied and best performing organic semiconductors to
date, crystallizes in three different polymorphs, namely,
orthorhombic, monoclinic, and triclinic. Only the orthorhombic form exhibits high charge carrier mobility.[23]
This example shows that charge carrier mobility is definitely a material and not solely a molecular property.
However, the attainable polymorphic forms of a given
compound evidently depend on its molecular structure.
Figure 1 presents a selection of molecular structures of p
systems that give rise to impressive charge carrier mobilities, approaching or even overcoming 10 cm2 V1 s1. Naturally, the highest values of mobility are obtained on
single crystals.[17–22,24,25]
It is important to keep in mind that very high charge
carrier mobility values could result from unintentional experimental errors or data misinterpretation. None of us
are experts in electrical measurements and feel sufficientIsr. J. Chem. 2013, 53, 1 – 27
ly confident to validate literature results. The task is impossible because of the vast diversity of measurement
conditions. Nevertheless, a commonsense principle applies: measurements under comparable conditions must
have been reproduced by at least two independent
groups. Applying this strict criterion, the mobility values
of pentacene (1), triisopropylsilyl (TIPS)-pentacene (3),
rubrene (4), and benzothienobenzothiophene (5) are 2–3,
1.8, 20, and 9.1 cm2 V1 s1, respectively.[54] The highest
values of charge carrier mobility are, however, all reported herein because many of them are recent and have not
yet got the opportunity to be reproduced. It is likely that
other compounds that have been set aside based on preliminary and disappointing charge carrier mobility measurements could compete with or even outperform those
of the compounds shown in Figure 1, if they crystallize
into other polymorphic forms.[32] Note that hole and electron charge carrier mobility are considered together
herein, since their transport properties do not involve different physical concepts.[55,56] Herein, we deal with a burning question upon which the research programs of many
materials chemists, device engineers, and solid-state physicists is based: What currently limits charge carrier mobility in crystals of molecular semiconductors? The ques[a] G. Schweicher, Y. H. Geerts
Laboratoire de Chimie des Polymres, Facult des Sciences,
Universit Libre de Bruxelles (ULB), CP 206/1
Boulevard du Triomphe, 1050 Bruxelles (Belgium)
e-mail: [email protected]
[b] Y. Olivier, V. Lemaur
Service de Chimie des Matriaux Nouveaux
Universit de Mons, Place du Parc, 20
7000 Mons (Belgium)
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Guillaume Schweicher received his
Master in Chemical Engineering (2008)
and Ph.D. (2012) from the Universit
Libre de Bruxelles (ULB) under the supervision of Yves Geerts. He then
joined the group of Zhenan Bao at
Stanford University (USA) for a oneyear postdoctoral stay. Since January
2014, he is back at ULB. His current research focuses on the control of the
nucleation and growth of organic semiconductors through the use of solution
and thermal processing methods to
produce high-performance electronic
devices.
Yoann Olivier has been a postdoctoral
researcher in the Laboratory of Chemistry of Novel Materials since 2009.
During this period, he completed
a one-year postdoctoral stay with Profs.
H. Sirringhaus and R. H. Friend at the
University of Cambridge and several
short stays with Prof C. Zannoni at the
University of Bologna. His main research interests deal with the interplay
between the structural organization of
pi-conjugated materials and their optoelectronic and charge-transport properties using a combination of quantum chemical calculations, molecular mechanics/dynamics and kinetic Monte Carlo simulations.
Vincent Lemaur obtained his Ph.D.
from the University of Mons (Laboratory for Chemistry of Novel Materials) in
2005. He is now a Research Scientist
at the University of Mons. His research
topics deal with the study of the conformational and/or opto-electronic
properties of small organic (conjugated) molecules and polymers by combining molecular mechanic techniques
with quantum-chemical approaches.
Yves Henri Geerts was born in Brussels
in 1967. He accomplished his diploma
studies with Jean-Pierre Sauvage at the
Universit Louis Pasteur in Strasbourg,
France. In 1993, he obtained his Ph.D.
degree from the Universit Libre de
Bruxelles (ULB), Belgium. After postdoctoral stays with Klaus Mllen at the
Max Planck Institute for Polymer Research (MPIP) in Mainz, Germany, and
Richard Schrock at MIT in Boston,
USA, he accepted a FNRS position at
ULB, in 1997. He was appointed Professor at the same university in 1999. His current research focuses
on the synthesis, self-assembly and processing of molecular semiconductors.
Isr. J. Chem. 2013, 53, 1 – 27
tion reveals a twofold practical and fundamental importance that is better appreciated if molecular semiconductors are benchmarked with other semiconducting materials. Engineered AlGaAs/GaAs heterostructures grown by
molecular beam epitaxy afford incredible mobility values
of about 35 000 000 cm2 V1 s1.[57] Graphene and carbon
nanotubes exhibit high charge carrier mobility on the
order of about 100 000–200 000 cm2 V1 s1.[58–61] Single
crystals of silicon have a mobility of about
1200 cm2 V1 s1.[62] Then come oxides with room-temperature mobility values of about 200–400, 160, and
240 cm2 V1 s1 for single crystals of ZnO, In2O3, and
SnO2, respectively.[63] Although they have some disadvantages, they represent serious contenders to organic semiconductors for transistor applications.[64–66] Molecular
semiconductors and conjugated polymers show a mobility
ranging from 1 to 43 cm2 V1 s1 for the best performing
ones.[8,14,34,39] Molecular semiconductors are by definition
molecules that are held together by weak van der Waals
forces; typically the molar cohesive energy per CH2
group in crystals of long alkanes is around 73 meV,[67]
which must be compared with kBT (26 meV at room temperature). For the sake of comparison, the electronic coupling, J, between adjacent p systems in crystals ranges
from 10–100 meV for most systems with two-dimensional
charge transport.[68] The thermal agitation manifests itself
by intramolecular (local phonons, specifically torsion
modes)[69] and intermolecular vibrations (nonlocal phonons).[70,71] Molecular systems appear, thus, as particularly
disordered semiconductors in comparison to their inorganic counterparts.[72–75] This explains their modest charge
carrier mobility relative to that of semiconductors held
together by ionic or covalent interactions. Then, why is so
much interest paid to molecular semiconductors? There
are several answers to this question: 1) molecular semiconductors have reached a mobility that equals and even
overcomes that of amorphous silicon (0.5–1 cm2 V1 s1);
2) synthetic organic chemistry offers an unbeatable access
to nearly endless structural variations; 3) molecular semiconductors are multifunctional materials, for example,
they intensely absorb or emit light and transport charges;
4) they are soluble, allowing the fabrication of electronic
devices on any substrates by simply printing them from
inks at near-ambient pressure and temperature; and 5)
charge carrier mobility of molecular semiconductors has
spectacularly improved over the last three decades, increasing from m 105 cm2 V1 s1, in the 1980s,[76,77] up to
43 cm2 V1 s1 nowadays.[7,8,16,34,39,78] Do the topics of molecular semiconductors, charge transport, and field-effect
transistors (FETs) need an additional review article?
Probably not. Several recent, comprehensive, and highquality reviews on synthesis, molecular systems, device
fabrication, and charge transport have been published,[5–10,12,14,16–22,34,78–91] in addition to several books.[1–4]
The goal of this paper, which deals with the question
given in the title, is rather different. It intends to be a crit-
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Figure 1. Highest values of charge carrier mobility reported for selected materials. R and R’ are either n-alkyl or phenyl groups. 1: 5–
40 cm2 V1 s1,[26,27] 2: 1–11 cm2 V1 s1,[28–31a,b] 3: 1–11 cm2 V1 s1,[5,6,32,33] 4: 5–40 cm2 V1 s1,[34,35] 5: 1.8–43 cm2 V1 s1,[7,36–39] 6:
17.2 cm2 V1 s1,[40] 7: 2.8–11 cm2 V1 s1,[41–46] 8: 3–16 cm2 V1 s1,[47,48] 9: 3.6–9.5 cm2 V1 s1,[49] 10: 7–11.2 cm2 V1 s1,[50] 11: 1–10 cm2 V1 s1,[51]
12: 3.3–15.6 cm2 V1 s1,[52] 13: 3.5–10.2 cm2 V1 s1.[53]
ical discussion that asks more questions than it provides
answers. As a consequence, this paper often reflects the
personal opinion of the authors and the reader is evidently free to agree or disagree. It also intends to confront
theoretical and experimental approaches towards better
performing functional materials. The scope is voluntarily
limited to molecular semiconductors; the vast and interesting field of conjugated polymers is excluded. The interested reader is directed to recent review articles dealing
with this topic.[16,78,92,93] The review is divided into three
main sections: theory, materials, and measurements.
2 Theory
2.1 Hopping versus Band-like Models
As reported above, the charge carrier mobility of many
small organic p-conjugated molecules has now reached
and exceeded values of 1 cm2 V1 s1, which were seen as
critical to achieve devices ready for commercialization,
especially for FET applications that act as logic operators
in electronic circuits. Controlling charge transport at the
molecular scale, namely, being able to predict the charge
Isr. J. Chem. 2013, 53, 1 – 27
carrier mobility of an organic semiconductor from its
chemical structure is a hard, nearly impossible, task. Specifically, in this related issue, the bottleneck remains the
prediction of the organization of the molecules within, for
instance, the transistor channel or, in a more broad scope,
the crystal structure.[94] Few studies so far have been able
to predict the crystal structures of small organic p-conjugated molecules, usually starting from a well-known molecular crystal structure and predicting the crystalline organization of potentially interesting derivatives.[48] Another important aspect is related to the large difference in
magnitude of the charge carrier mobility, which makes it
almost impossible to build a single theoretical model for
both amorphous and crystalline materials. The discussion
around the charge-transport mechanism is often related
to the temperature dependence of the charge carrier mobility. It is now well established that two extreme pictures
exist.[56] First, band (or coherent) transport, which is characterized by a decreasing charge carrier mobility as the
temperature increases (m / T-a with a > 0), and is typical
of inorganic semiconductors, such as silicon. In p-conjugated materials, such behavior has only been observed on
a few occasions in ultrapure single crystals[95–97] over
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a large range of temperatures. In this transport regime,
the wavefunction of the charge carriers (hole or electron)
is delocalized over several molecular units. Charge diffusion proceeds quickly throughout the crystal and is limited by the lattice phonons scattering. The mobility is evaluated as:
m¼
et
m*
in which t is the charge carrier scattering time and m* is
the effective mass of the electron or hole. Second, the
hopping (or incoherent) regime where the charge carrier
mobility is typically thermally activated (m / exp(DG/
kBT) with DG > 0) and the wavefunction of the charge is
localized on a single molecule. In some instances,[98,99] it
has been observed that charge carrier mobility in conjugated materials exhibits thermally activated behavior at
a lower temperature, reaching a maximum followed by
a decrease at higher temperature. Interestingly, the lowand high-temperature behavior has been associated with
hopping and band regimes, respectively, and the transition
between the two regimes is called the bandhopping
crossover.
2.2 Charge Transport: Microscopic Parameters
At the microscopic scale, charge transfer is usually described by two parameters, namely, the transfer integral,
J, and the reorganization energy, l. When looking at
charge transfer between two molecules M1 and M2, the
transfer integral represents the interaction between the
wavefunctions of the configuration corresponding to the
charge initially localized on M1 and the configuration
where the charge is localized on M2 after charge transfer.
The transfer integral is seen to promote charge delocali-
zation in the molecular complex formed by M1 and M2.
From a computational point of view, J is often evaluated
at a quantum-chemical level, in a one-electron picture, as
the matrix element:[100–102]
J ¼ M1 jV jM2
in which fM1 and fM2 represent the HOMOs (LUMOs) of
molecules M1 and M2, respectively, and are highly sensitive to the respective orientation of the molecules involved in charge transfer (see Figure 2).[103–106] On the
other hand, the reorganization energy tends to localize
the charge carrier on a single molecule. This parameter is
the sum of two contributions, namely, the internal (li) and
external (lS) reorganization energies, which account for
the change in the geometries of the molecules involved in
charge transfer and the change in the polarization of the
surrounding medium, respectively. Interestingly, the magnitude of the internal contribution is highly sensitive to
the chemical structure of the molecule. For instance, it
was shown previously using quantum-chemical methods
that the substitution of a triphenylene core by a methoxy
group increases li from 180 to 330 meV, while thiol substitution barely impacts the reorganization energy (li =
160 meV), highlighting the significant impact of the
choice of side groups on charge transfer.[105] The magnitude of lS in organic crystals appears to be lower than the
internal contribution (in anthracene, lS is 4[107] or
44 meV,[69] while using a polarizable force field and
Austin Model 1 (AM1) level, respectively, compared with
137 meV[108] at the density functional theory (DFT) level
and 303 meV[69] at the AM1 level for li). In solution, depending on the dielectric constant of the solvent, lS can
however exceed li in some cases.[109] When considering
the charged molecular complex (M1M2) + /, in which M1
Figure 2. Evolution of the electronic splittings (= 2J) calculated at the INDO level of the HOMO and LUMO levels in a perfectly cofacial
dimer formed by two sexithienyl molecules separated by 4 as a function of the degree of translation of one molecule along its mainchain axis. Adapted from ref. [103].
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and M2 are equivalent, localization (delocalization) effects that occur in the hopping (band) regime are defined
as a function of the relative magnitude of the transfer integral, J, and the reorganization energy, l. In the strong
coupling regime (J @ l), the charge is delocalized between
M1 and M2 and charge transport proceeds through a band
mechanism, while, in the weak coupling regime (J ! l),
charge is either localized on M1 or M2 and charge transport takes place following a hopping mechanism. In the
latter case, while adopting a classical picture, charge
transfer is vibrationally assisted, namely, M1 and M2 adapt
their geometries to reach the transition state and to allow
charge transfer to occur. The rate of charge transfer is
often described in first approximation in terms of semiclassical Marcus theory, which explicitly includes the contribution of the transfer integral and the reorganization
energy:[110]
khop
" 2 #
l þ DG0
2p 2
1
¼
J pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi exp h
4lkB T
4plkB T
in which DG0 is the Gibbs free energy of the chargetransfer reaction M1 + / + M2 !M1 + M2 + /. Note that
a partially and fully quantum treatment of the vibrational
spectrum exist and lead to the MarcusLevichJortner[111]
and Fermi golden rule expression,[112] respectively. Interestingly, in molecular organic crystals, J is often on the
same order of magnitude as l, which makes both mechanisms discussed above inapplicable for quantitative purposes, especially in determining the mobility temperature
dependence. Possibly in such regime, a band-like to hopping-like transport crossover can be observed.
2.3 What Limits Charge Carrier Mobility?
2.3.1 Static Disorder
Disorder is inherent to the production of organic electronic devices and particularly takes place through polymorphism, defects, impurities, high flexibility of the molecules, and electrostatic effects (local dipoles). In polycrystalline films, grain boundaries are known to reduce
charge carrier mobility values by limiting the current
transmission between crystallites, allowing for a limited
number of conduction channels or by trapping charges at
the interface between the crystalline grains. Another
source of disorder comes from possible contamination by
impurities that could act as traps and slow down the
charge carrier on its way. A direct consequence of disorder is the strong tendency for charges to localize spatially
on the trapping sites. Geometrical relaxation takes place
on the picosecond timescale around the charged molecule, leading to the formation of a polaron, namely, the
charge carrier and its associated deformation of the surrounding nuclei, and charge transfer happens through
a hopping mechanism.[113] Disorder is usually divided into
Isr. J. Chem. 2013, 53, 1 – 27
two contributions: energetic and positional disorders.[114]
Energetic disorder accounts for the distribution of the socalled site energies that correspond to the density of
states (DOS), that is, the distribution of the transport
level energies, namely, the HOMO (LUMO) of the individual molecules. The DOS is characterized by either
Gaussian or exponential distributions with widths defined
by the parameters s and T0, respectively. Typical values
of s and T0 in amorphous films are on the order of 0.1–
0.15 eV[115] and 300–600 K,[116–118] respectively. Without
entering into too much detail, recently, various approaches on going from classical Coulombic interactions,[119] polarizable force fields,[120] to a microelectrostatic
model[121,122,114] have tried to rationalize the origin of the
energetic disorder from a molecular perspective. On the
other hand, positional disorder describes the distribution
of relative orientations of the molecules involved in the
charge-transfer process and is related to the distribution
of the transfer integral that is also characterized by
a Gaussian distribution of a width equal to S when referring to the Gaussian disorder model (GDM) developed
by Bssler.[123]
2.3.2 Dynamic Disorder
In the case of organic single crystals, the hopping picture
no longer holds because of the absence of static disorder
and the transfer integral is on the same order of magnitude as the reorganization energy, which leads to situations where the charge carriers are delocalized on a small
number of molecules.[124] Indeed, delocalization on
a mesoscopic scale is hampered by both intra- and intermolecular vibrations, also recalled as electronphonon
coupling. A classification scheme for the various limiting
types of charge carrier transport can conveniently be obtained with the following vibronic Hamiltonian:[125]
H ¼ H el þ H nucl þ H loc þ H nonloc
Hel is the electronic Hamiltonian that contains the
terms related to the energies of each molecular site (en)
and the transfer integrals from sites m to n, Jmn. Hnucl accounts for the vibrational spectrum represented, typically,
by a vibration j of energy hwj. Hloc describes the local
electronphonon coupling, as described in Holsteins
model,[134,135] namely, the modulation of sites energies en
due to the electronphonon interactions, which is also
known as dynamic diagonal disorder. The electron
phonon coupling constant, gj, defines the magnitude of
the interaction between electron and phonon through vibrational mode j. Hloc includes implicitly the intramolecular li and intermolecular lS contributions to the reorganization energy. Hnonloc describes the modulation of the
transfer integral, Jmn, due to the electronphonon interactions and is referred to as a nonlocal coupling that reflects the dynamic off-diagonal disorder and fj determines
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the magnitude of the local electronphonon coupling of
vibrational mode j. Hnonloc is the key interaction in
a Peierls-type model, such as the SuSchriefferHeeger
Hamiltonian for conducting polymers.[126] In organic molecular crystals, no static disorder is considered and all
site energies are set to a unique value, e. Among the contributions to the vibronic Hamiltonian, Hel favors coherent transport and delocalization of charge carriers, as discussed in the previous section. On the other hand, Hloc
and Hnonloc, by considering electronphonon couplings, introduce incoherent transport. Depending on the magnitudes of these different contributions to the vibronic
Hamiltonian, we can distinguish three different transport
mechanisms: 1) Hel contribution is larger than Hloc and
Hnonloc. In this case, the transfer integral between adjacent
molecules is relatively large compared with the other energies, Jmn @ hwj, gj · hwj, fj · hwj, and kBT, and charge
transport proceeds through a band mechanism. 2) Hloc
and Hnonloc contributions are much larger than Hel. The
transfer integral is much smaller than the electron
phonon coupling. As a consequence, charge carriers are
localized due to intra- and intermolecular vibrations and
charge motion consists of a series of uncorrelated hops. 3)
Hel contribution is comparable to Hloc and Hnonloc. The
transfer integral is comparable to the variations induced
by dynamic disorder.[127,119] This is typically the case for
organic molecular crystals. Both band-like and hopping
pictures fail to reproduce the complete temperature dependence observed for many different crystals. Calculating charge-transport properties in organic molecular crystals is a challenging task, since electron and nuclei
(phonon/vibrations) motions are coupled together.
2.4 Molecular Crystals: Transport Model
As a first approximation, charge transport in organic molecular crystals has often been described within the hopping regime. Most of the models developed rely on
a bottom-up approach,[112,119,128] where the transfer integrals between pairs of molecules and the reorganization
energy are estimated at the quantum-chemical level and
then plugged into a rate expression such as the Marcus
hopping rate. The relative positions and hopping rates between nearest neighbor molecules are finally used to calculate the charge carrier mobility (from the total distance
and hopping time) with Kinetic Monte Carlo simulations.
In addition, the influence of electronphonon coupling
on the magnitude of the charge carrier mobility is often
studied by combining molecular dynamics simulations,
quantum-chemical calculations of the transfer integrals,
and Kinetic Monte Carlo simulations.[119,128,129] For instance, it has been shown with such an approach that new
pathways for charge transport could be opened up due to
nonlocal electronphonon couplings.[119] Even though
considering incoherent transport does not lead to quantitative agreement in terms of charge carrier mobility or
Isr. J. Chem. 2013, 53, 1 – 27
temperature dependence, it allows, in many cases, the difference in mobility between compounds of one
family[130,131] to be rationalized, as well as the charge mobility anisotropies[132] measured experimentally.[2,133] However, for quantitative agreement with experiments, charge
transport in molecular crystals has to include both coherent and incoherent contributions, especially to reproduce
the evolution of charge carrier mobility over the full
range of temperatures. When looking at the models that
have been developed recently, we can distinguish between
polaron models and approaches based on numerical simulations. Polaron models are based on the development,
within a quantum framework, of mobility expressions
depending on parameters (transfer integrals, site energies and local and nonlocal electronphonon coupling
constants) that are usually evaluated with the help of
quantum-chemical methods. Interestingly, polarons are
explicitly considered as the quasi-particle responsible
for conductivity in organic crystals. After the seminal
work of Holstein,[134,135] the approach has been extended
to account for local and nonlocal electronphonon couplings, still in the narrow-band approximation, which implicitly considers that charge carriers are strictly localized
on a single molecule (small polaron approximation).[136–138] Hopping and band-transport contributions
are considered on the same footing and are not evaluated
separately.
However, this theory does not predict a finite mobility
value for naphthalene single crystals at low temperature,
but correct temperature dependence (Figure 3) because
of the renormalization of the transfer integral, which accounts for the dependence on electronphonon coupling
and temperature. More recently,[139,140] extension of the
previous model to the finite bandwidth limit, considering
only explicitly local coupling, leads to finite mobility at
low temperature for naphthalene. Nonlocal effects and
other scattering effects (static disorder) are included in
the polaron lifetime, which implies that the total mobility
is the sum of coherent (band-like) and incoherent (hopping-like) mobilities. On the other hand, numerical simulations of charge transport are based on a similar vibronic
Hamiltonian that accounts for local and nonlocal couplings with the exception that nuclei dynamics are treated
classically. Nuclei dynamics and electronic (adiabatic)
state characterizing the system are then readily obtained
by solving the classical Newton equations concomitantly
with the electronic (time-dependent Schrçdinger) equation.[141–143] One of the most important successes of these
theories is the good agreement in terms of mobility range
and decreasing evolution of mobility when increasing the
temperature due to both the modulation of the transfer
integrals and the change in site energies.[144] Recently, it
has been evidenced that the last approaches are equivalent to a mean field theory, and thus, do not allow band
hopping crossover to be reproduced. Indeed, in this
model, electron dynamics occur on a single adiabatic
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Figure 3. Hole mobilities in naphthalene. Comparison between experimental data (middle) and narrow-band (right) and finite-band theories (left); the different colored lines represent the temperature dependence along the different crystalline directions. Left: Both coherent
(dashed line) and incoherent (dotted line) contributions to charge transport are reported. Adapted from ref. [140]. Copyright 2011 WileyVCH Verlag GmbH & Co. KGaA, Weinheim.
energy surface, which is averaged over the different adiabatic states of the system. Transitions between these
states are not considered (neglecting nonadiabatic couplings in the electronic equation), which might lead to
both incorrect state population statistics and electron dynamics. A direct consequence is that the charge wavefunction is spread over all sites and is always delocalized,
which implies that no charge localization can be observed. Interestingly, by considering explicitly the contri-
bution from the nonadiabatic couplings,[145] both the
band-like picture and the hopping-like picture can be reproduced (Figure 4); this highlights the crucial influence
of nuclei dynamics on electron dynamics. In addition, the
influence of nonlocal couplings is also reproduced,
namely, charge carrier mobility is reduced if the nonlocal
coupling contribution is turned on when band-like transport is expected (electronic couplings reorganization
energy), while it is increased when hopping-like transport
Figure 4. Temperature dependence of the (A) charge carrier mobility and (B) localization length for a model one-dimensional stack. The
different curves are obtained for different values of the transfer integral t and nonlocal electronphonon couplings b. Reprinted with permission from ref. [145]. Copyright 2014 American Chemical Society.
Isr. J. Chem. 2013, 53, 1 – 27
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is observed (electronic couplings are smaller than the reorganization energy).
2.5 Dielectrics: Influence of Local Electrostatic Disorder
Most of the studies reported so far have dealt with bulk
transport and have not considered the particular case of
OFETs where charge transport occurs close to the insulating dielectric layer. The latter is usually an oxide or
a polymeric layer that is vapor-deposited or spin-coated,
respectively. The morphology at the dielectricorganic
semiconductor interface can be influenced by the deposition of both materials and leads to some interface roughness, which can negatively impact charge transport. However, when intrinsic charge-transport features can be extracted, charge carrier mobility appears to decrease when
the dielectric constant of the insulating layer increases.[146]
In particular, it has been shown in thin-film transistors
of 1 that hole mobility is four times larger when the
organic semiconductor is deposited on top of polystyrene (PS) compared with poly(methyl methacrylate)
(PMMA).[147,148] Understanding the difference in hole mobility in these two cases requires an atomistic description
of these two interfaces. Molecular dynamics simulation
studies have been performed to simulate a realistic interface between PS (PMMA) and four layers of crystalline
1. The simulations showed that the interfaces generated
were similar and the difference in hole mobility was
therefore not expected to come from morphological considerations, but instead to arise from the difference in
energy landscapes experienced by a hole resulting from
the different electrostatic environments generated by the
polymeric layers. Interestingly, the distributions of energetic disorder in the layer of 1 close to the organicdielectric interface appears to be wider for PMMA than for
PS because of the presence of strong local dipoles (e.g.,
from carboxyl and methoxy groups) within the PMMA
dielectric layer.[119] In contrast, it is similar for both interfaces within the second layer of 1 pointing towards the
local character of the influence of the polymeric layer.
Based on these energy landscapes, hopping transport simulations within the layer of 1 in contact with the polymer
have been performed and have shown 12 times larger
hole mobilities for the 1/PS interface relative to the 1/
PMMA interface, in good agreement with experiments.
Different solutions have thus been investigated to decouple the interfacial impact of the insulating layer on the
charge-transport properties of the organic semiconductors
by either functionalizing the dielectric with a self-assembled monolayer or by considering compounds with long
alkyl side chains.[54,149]
2.6 Charge Density
The consideration of the charge density dependence of
charge carrier mobility is crucial to reproduce the I/V
Isr. J. Chem. 2013, 53, 1 – 27
characteristics of single charge carrier diodes as well as
FETs.[116] This effect has been highlighted in disordered
materials, where it has been shown that, upon going from
a diode type of device (low charge density case) to a FET
(high charge density), the hole mobility in poly(3-hexylthiophene) and some derivatives of poly(paraphenylenevinylene) has been seen to increase by one and three
orders of magnitudes, respectively.[150] This significant
effect of charge density on charge-transport properties
has been included in the Extended Gaussian Disorder
model based on a hopping picture.[151] In this model, the
mobility is expressed as a product of density-dependent
and density-independent terms:
mðT, 1, EÞ mðT, 1Þ f ðT, EÞ
The increase in charge mobility has been interpreted
with this model and explained by the enhancement of the
density-dependent terms accounting for the filling of the
bottom of the Gaussian DOS, which allow access to regions of the DOS where typically more states are available.
2.7 Is a Nonequilibrium Approach Needed?
As a general matter of fact, quantum mechanics is the
major theoretical frame of the current understanding of
the charge transport of molecular semiconductors. Their
intrinsic thermal disorder has mostly been treated with
equilibrium statistical mechanics.[72–75] Any FET under operation is a dissipative structure that releases heat and
produces entropy.[152] In the nonequilibrium context, electronic circuits are of particular interest. Landauer has
demonstrated, in two seminal papers devoted to entropy
production in linear electrical circuits,[153,154] a counterexample to the minimum entropy production at stationary
state postulated by Prigogine. Instead, entropy production
at stationary state is maximum in linear electrical circuits
because of observables that are antisymmetrical under
time-reversal, as recently explained by Maes et al.[155]
However, an OFET is a macroscopic object that obeys
the rules of nonequilibrium thermodynamics.[156] Charge
transport causes heat dissipation and electrical current is
linked to heat flux.[157] An order of magnitude calculation
shows that an OFET dissipates about 107 J s1 during operation. This is not much in comparison to the processors
of computers, which dissipate typically about 100 J s1, for
the most recent ones that count about 109 transistors. The
same power dissipation of about 107 J s1 is roughly estimated for both FETs and OFETs. The important point is
not so much the absolute value of the dissipated power.
The relevant questions are as follows: 1) At which length
scale does heat dissipation occur?[158] 2) How does it compare to kBT? Typically, a charge motion from one molecule to the neighboring molecule along a field of 1–6
106 V m1 corresponds to an energy release of 0.4–
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2.4 meV, which takes place on a distance of 4–8 . Values
in the range of 0.4 to 2.4 meV are, however, lower than
the electronic coupling of many molecular semiconductors[159,160] 3) What is the role of reduced dimensionality?
4) How does heat flow in a system with very different
materials and interfaces in what concerns thermal conductivity?[161] Joules law has been used to calculate the
contact resistance by integrating the local dissipated
power over the whole volume of a transistor of 1. The distribution of dissipated power has been mapped and depends on gate voltage (Vg).[162] At room temperature,
metal electrodes have high thermal conductivity (gold,
L = 318 J K1 m1 s1) in comparison to organic semiconductors (0.6 L 2.1 J K1 m1 s1) and a dielectric polymer layer (0.1 L 0.5 J K1 m1 s1).[163,164] Interface thermal conductance (J K1 m2 s1), not to be confused with
thermal conductivity (J K1 m1 s1), must be considered
too, notably between metal electrodes and molecular semiconductors; an interface for which moderate
thermal conductance is anticipated, that is, about
1 107 J K1 m2 s1.[161,165,166] 5) On which timescale is heat
dissipated versus the characteristic residence time of
a charge on a molecule? Heat dissipation probably occurs
at comparable timescales, in the range of 0.1 to 10 ps, depending on the systems.[73,72,167] These questions appear
pertinent to us. The justification comes from the bias
stress that is commonly observed in OFETs. In thermodynamic language, an OFET is an open system that exchanges energy and matter (electrons) with its surroundings. When it is switched on, it is far away from equilibrium and relaxes to the steady state through fluctuations.[152] Immediately, new questions appear. To which
extent are electrical current and heat flux coupled? What
induces bias stress at the molecular level? Do structural
rearrangements occur at crystallographic defects of the
semiconductor or in the dielectric layer? What is the role
played by impurities?[168] We ignore these answers, tut
two things are certain: On the one hand, OFETs are fundamentally different from FETs because Si exhibits a thermal conductivity of 150 J K1 m1 s1,[161] whereas that of
organic
semiconductors
is
on
the
order
of
1 J K1 m1 s1.[163,164] On the other hand, thermoelectric
devices made of conducting polymers show that heat flux
and charge transport are linked.[169–171] There is no reason
that OFETs behave differently at the thermodynamic
level. It is worth mentioning, here, the work of Crispin
et al. who used an organic electrochemical transistor to
study the thermoelectric power factor of conducting polymers.[172] The field of organic electronics would benefit
from more theoretical work conducted in the frame of
nonequilibrium thermodynamics and statistical mechanics.[157,173]
Isr. J. Chem. 2013, 53, 1 – 27
2.8 Is There a Theoretical Limit?
It is concluded from this section that charge carrier mobility is not a scalar, but a mathematical function of time
and temperature. Another conclusion is that modeling
charge transport in organic crystals for quantitative purposes, namely, predicting intrinsic charge carrier mobility,
requires accounting for the coupling between electron
and nuclei dynamics and their mutual influence on their
respective dynamics. Crystal structure prediction remains,
at the moment, the bottleneck in allowing the design,
from first-principles prediction, of molecular semiconductors with exceptional charge-transport properties. In particular, there is no reason, from the first principles of
chemistry and physics, to believe that the charge carrier
mobility is limited to the current values of
43 cm2 V1 s1,[35,39] or 20 cm2 V1 s1 if applying reproducibility criteria.[54] For instance, a careful fine-tuning of molecular structures that would lead to a decrease in electronphonon coupling is certainly desired for the community of organic electronics to reach upper charge carrier mobility values. The race to higher charge carrier mobility in molecular semiconductors also represents
a formidable opportunity to gain more theoretical understanding.
3 Materials
In the last two decades, enormous synthetic effort has
been produced to diversify the structure of p systems, to
investigate their solid-state packing, and to probe their
charge-transport properties. We present herein a broad,
and intentionally not too detailed, overview of functional
materials based on principles, orders of magnitude, and
most salient results. The goal is to try to extract major
trends from which intuitive design principles could be deduced.
3.1 Best Performing Molecular Structures
It is now opportune to come back to the role of molecular structure on charge carrier mobility that has been
evoked in the Introduction. Pentacene (1)[10,174–183] and
fullerene (2)[28–31a,b,184–186] are often used as benchmarks for
charge transport. References are far too numerous to cite
them all; the readers are thus directed to excellent reviews.[8,9,11,16,34,187,188] Note that derivatives of 2 have always
demonstrated inferior charge-transport performances in
comparison to C60. Typically, [6,6]-phenyl-C61-butyric acid
methyl ester (PCBM) exhibits m 102 cm2 V1 s1 for
both holes and electrons.[189] One of the reasons is probably that PCBM requires special conditions to form mm
size crystals.[190] Another reason is that local dipoles
induce energetic disorder.[191] Conversely, some derivatives of 1 perform very well. 6,13-Dichloropentacene
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forms microribbons that exhibit a charge carrier mobility
up to 9 cm2 V1 s1.[192] TIPS-pentacene (3) is one member
of a large family of compounds synthesized in the group
of Anthony, in recent decades. Homologous series of
acene derivatives, synthesized by this group, have majorly
contributed to advance the field of charge transport in
molecular semiconductors, notably by clarifying the intimate relationship between molecular and crystal structures. Another famous member of the family is bis[tri(ethylsilyl)ethynyl]anthradithiophene, known as TESADT, which has comparable charge-transport properties
to 3.[5,6,10,32,33,43,75,185,193–201] The most elaborated of the compounds produced by the group of Anthony is likely to be
bis[tri(isopropylsilyl)ethynyl]difluoroanthradithiophene
(diF-TEG-ADT), which exhibits an average mobility of
2.3 cm2 V1 s1, in polycrystalline films.[202] Rubrene (4) is
probably the compound that has been studied in most
detail for its optoelectronic properties.[34,43,203–219] There
are, however, only a limited number of derivatives of
4,[23,220–223] with the noticeable exception of fully deuterated 4 reported recently by Frisbie et al.[224] Then come
[1]benzothieno[3,2-b][1]benzothiophenes (BTBTs), dinaphtho[2,3-b : 2’,3’-f]thieno[3,2-b]thiophenes (DNTTs),
and
dianthra[2,3-b : 20,30-f]thieno[3,2-b]thiophenes
(DATTs), among which 5–8 (Figure 1) are the most representative compounds put forward by the group of
Takimiya. Their outstanding transport properties associated with their chemical stability and relatively easy synthesis have generated numerous physical studies.[7,36–42,44–48,74,225–239] One of the DATTs with a high-mobility aromatic core introduced into the arena of organic
electronics is V-shaped dinaphtho[2,3-b : 2’,3’-d]thiophene
(9). This compound and other similar structures are abbreviated as DNT-Vs.[49] The only member of the tetrathiafulvalene family, which has achieved a mobility of
above 10 cm2 V1 s1, is hexamethylenetetrathiafulvalene
(HMTTF; 10).[50] Phthalocyanines form an important
class of industrial pigments, known for their chemical stability. They offer the additional advantage that a metal
atom can be incorporated into the center of the molecules. When TiO is introduced into the structure, the resulting phthalocyanine derivative 11 is forced to adopt
a kind of brick wall packing favorable to high charge carrier mobility. Recently, Kurihara et al. reported bis(benzothieno)naphthalene (BBTN) derivatives 12 that showed
a mobility as high as 15.6 cm2 V1 s1 for polycrystalline
films.[52] At the same time, Yasuda et al. demonstrated
that single crystals of dithieno[3,2-b:20,30-d]thiophene
(DTT) core 13 exhibited a mobility up to 10.2 cm2 V1 s1
when it was flanked with phenyloctyl side chains.[53] One
direct observation, from Figure 1, is that molecules 1–10,
12, and 13 are weakly polar or nonpolar. It is easily understandable that strong dipoles will interact with charges
by electrostatic interactions and will slow them down.
This dipolar effect, well-known for dielectric layers,[146] is
discussed below. On the other hand, molecules with
Isr. J. Chem. 2013, 53, 1 – 27
strong dipoles interact much more strongly together.
Could stronger crystal cohesion increase charge transport? This question has been tackled by Wrthner et al.
and the answer was negative. The values of mobility for
merocyanine are rather modest, in the order of 0.1 cm2
V1 s1.[240] However, phthalocyanine 11 also exhibits
a dipole and very short intermolecular distances of 3.145
and 3.211 . Mobility values are honorable, ranging between 1 and 10 cm2 V1 s1.[51] A slightly different, but related, question is to know if molecular semiconductors interacting through hydrogen bonding could display high
charge carrier mobility? Values range from 0.2 to
1.5 cm2 V1 s1 for hydrogen-bonded analogues of tetracene and 1 have been recorded. A direct advantage of
this approach is that no fancy organic semiconductors are
needed, since industrial pigments such as epindolidione
and quinacridone are used.[241] A disadvantage is that hydrogen bonding extends over short distances that are not
commensurable with that observed for a herringbone arrangement. This tends to induce cofacial packing and
one-dimensional charge transport that is highly sensitive
to any defect in the crystal structure.[68] The role of quadrupolar interactions has also been recently discussed in
relation to band-like transport.[54] Note that clever molecular design allows the synthesis of nonpolar molecules
with a short contact between p systems. A distance between cofacial p systems as short as 3.24 has recently
been reported for a triethylgermylethynyl-substituted anthradithiophene that exhibits an average mobility of
2.3 cm2 V1 s1 over 104 devices and the highest value of
5.4 cm2 V1 s1.[202]
3.2 Molecular Design from Theory versus Experimental Results
The theoretical section teaches us that molecular structure determines reorganization energy and that the latter
has to be as low as possible to facilitate charge transport.
However, no strong correlation between l and m is experimentally observed. Phthalocyanine, which exhibits l =
45 meV for holes,[242] that is, one of the lowest values of
molecular semiconductors and roughly half the value calculated for 1 (l = 100 meV) or 4 (l = 88 meV), reaches
only a mobility of 0.0026 cm2 V1 s1.[78] Additional examples come from oligomeric series of acenes and diacenefused thienothiophenes, for which longer oligomers with
the lowest l do not exhibit the highest charge carrier mobility.[5–7,9,47,48] Among other things, molecular structure
also determines the packing of organic semiconductors,
and therefore, their transfer integrals. They are often calculated,[7,47,48,230,243] but, in some cases, they have also been
measured and importantly theoretical and experimental
values agree quite well.[244] Let us restrict the discussion
to crystal structures that are either of the herringbone or
brick wall type.[5–7] Even for these favorable crystal arrangements, several transfer integrals are calculated
within the plane of the substrate and charge-transport
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characteristics are anisotropic, while occurring in two dimensions. As for l, the link between J and m appears to
be rather loose.[24] A comparison of the J and m values of
BTBTs (J 50–60 meV, 1.8 m 43 cm2 V1 s1) with that
of DNTTs (J 70–80 meV, 1 m 11 cm2 V1 s1) speaks
for itself.[7,36–39,41,42,45,47,48] These observations are not surprising, l and J describe molecular semiconductors at the
nanoscale, whereas charges have to cross the full channel
length, typically about 10 mm, to go from source to drain.
The distance of 10 mm is better understood if expressed
in number of unit cells (20000) or in number of molecules
(40000). Therefore, it should not be concluded that l and
J are irrelevant parameters. They do play a substantial
role on the ultimate values of mobility, but additional factors must be considered too.
3.3 What Are the Other Factors Limiting Charge Carrier
Mobility?
3.3.1 Purity, Traps, Defects, and Disorder
The first factor that comes to the mind, but that is often
neglected, is purity.[17,98,159,208,245,246] Note that traps are associated with impurities, as demonstrated by Karl et al.,
who voluntarily added minute amounts of impurities to
a semiconductor.[98] The same experiment was reproduced
by Hanna and Funahashi on a different system.[247] It was
evidenced that very limited amounts of impurities, on the
ppm level, were sufficient to hinder severely charge transport. Impurities result from synthesis, contamination, and/
or chemical degradation. The examples of 1 and 4 are illustrative. Pentacene (1) is often contaminated by pentacenequinone, which is both a starting material and a photooxidation product.[97] It also contains other impurities,
such as benzothiophene; naphthalene; 6,13-dihydropentacene; and unidentified C22H24, C22H14O, C22H14O2, and
C22H16O2.[248] Rubrene (4) is contaminated by traces of
two impurities: one is active in OFETs, whereas the other
is not.[208] Note that traps can also be induced by photonassisted diffusion in 4.[212] Detailed purity studies have not
been conducted on 3 because the mobility remains more
or less the same, regardless of the number of various purification processes the compounds have been put
through.[249] TES-ADT shows that multiple sublimations
do not improve the performance of single-crystal devices
made from this class of compounds.[250] De Cupere et al.
analyzed, in depth, the inorganic impurities in soluble
phthalocyanine derivatives purified by column chromatography with hexane as the eluent. The compounds contained traces of colloidal silica-gel particles from the stationary phase.[251] Note that glassware used for synthesis
can also be a source of inorganic impurities, depending
on the reaction conditions.[245] Sublimation in a temperature gradient appears to be one of the most used purification methods, but it is limited to low-molecular-weight
compounds. Interestingly, this method is also used to
Isr. J. Chem. 2013, 53, 1 – 27
grow high-quality single crystals.[18,252] An old technique
that is still used nowadays is zone refining.[253–255] This
method is unfortunately rather sample dependent and requires optimization.[256] Regardless of the purification and
analytical methods used, the relevant question is how
does the concentration of electrically active impurities
compare with charge density? The order of magnitude of
charges at the semiconductor/dielectrics interface is
1 charge for 100–1000 molecules.[257,258] Typically, the detection limit of analytical methods is in the range of 1017
to 1018 inorganic impurities per cm3,[251] which means
there is 1 impurity for 500–5000 molecules calculated for
a typical semiconductor with a molecular weight of
500 g mol1 and a density of 1.2 g cm3. What is the proportion of electrically active impurities? Upon crystallization, molecular semiconductors naturally tend to expel
impurities from the molecular lattice. They are very likely
to be located at defects, at grain boundaries, and at interfaces.[97,259] The concentration of inorganic and organic impurities located at the semiconductor/dielectrics interface
remains an open question. Note that some electrically
active impurities could also come from the dielectric
layer or from the atmosphere. Water is the main culprit
behind the operational instability of OFETs.[260] A second
parameter that limits charge transport, even in single
crystals, is structural defects that also act as traps and
limit the reliability of OFETs.[87] They are always present
for obvious thermodynamic reasons and are of different
types: lattice vacancies or so-called Schottky defects, dislocations, and grain boundaries.[252] The density of lattice
vacancies in anthracene is about 1.5 1014 cm3, at 300 K,
which corresponds to 1 vacancy for about 3 109 molecules.
Step and spiral dislocations are formed when part of
a crystal is displaced relative to its neighborhood. Their
density is defined as the number of dislocation lines that
pass through a unit surface of the crystal. Thermal annealing is a good way to reduce their density to 10 cm2 ;
for crystals grown from the vapor phase that is the most
favorable case. Such a low density of defects matches that
of the best Si or Ge crystals. Recently, Takeya et al. quantified the density of defects for 4 from thermal conductivity measurements.[215] Bulk crystals grown from vapor,
bulk crystals grown from solution, and film-like crystals
grown from vapor exhibit defect densities of 2.5 1015,
5.1 1015, and 1.3 1016 cm3, respectively.[215] Real crystals
are not as perfect as one may imagine, at first glance.
They are composed of small crystallites, also called
mosaic blocks, with typical sizes in the range of 100 to
1000 lattice constants. The blocks are tilted relative to
one another by a few minutes of arc and small-angle
grain boundaries are formed at the intersection of blocks.
Single crystals of 4 have been investigated in detail by
Chapman et al. using X-ray diffraction and topography.[209] Rocking curve widths of different samples ranged
from 0.013 to 0.1508 for the full-width at half-maximum
(FWHM). The lowest value (0.0138) corresponds to
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a grain size of 3 mm, that is, in the range of the channel
length of OFETs. An important conclusion from this
work is that conventional polarized optical microscopy
(POM), although easy to use for initial screening, has insufficient resolution (in the order of 0.58) to assess crystal
quality for OFETs. The characterization of crystal defects
is a long-standing issue for both organic and inorganic
semiconductors.[261,262] What is new is that characterization
methods have dramatically improved thanks to synchrotron radiation and microscopy techniques. The interested
reader is directed towards excellent reviews[263–266] and
recent publications.[75,267] The abundance of diffraction
data has also favored their quantitative analysis with notions such as cumulative and noncumulative disorder or
paracrystallinity.[268] Unsurprisingly, these techniques have
demonstrated that grain boundaries considerably limit
charge transport.[176,178,269–271] One way to decrease the negative influence of grain boundaries is to blend molecular
semiconductors with conjugated polymers.[82,194,272] A final
type of defect that occurs only in low-symmetry molecules, such as TES-ADT and 2,3-dimethylnaphthalene, is
dipolar disorder, that is molecules assume reversed orientations to a lattice with similar or even identical lattice
energy.[98,252,273,274]
3.3.2 Polymorphism
Polymorphism is the occurrence of two or more crystallographic forms for a given compound.[275,276] Polymorphic
forms differ from one another by only a few kJ mol1. Do
the presence and number of crystallographic defects correlate with the existence of several polymorphs? In other
words, are compounds that exhibit rich polymorphism
more prone to having defects in their crystal structure?
We do not have the answer, but notice that naphthalene,
that is, a compound that has abundantly and successfully
been studied for its charge transport,[252] is also known for
not showing any evidence of polymorphism.[276] A counterexample is evidently 4, as stated in the Introduction.
Are all polymorphic forms equal? Certainly not: some
polymorphs are closer energetically and structurally. As
a matter of fact, the polymorphism of molecular semiconductors has certainly been less studied than that for pharmaceutical compounds.[277] It is only recently that the
Hirshfeld surfaces, a powerful tool to analyze and compare crystal structures,[278] have been used for molecular
semiconductors.[23,279] In this context, it is worth mentioning the work of Brillante et al., who used lattice phonon
Raman microscopy to assess the phase purity of what appeared at first glance as “monocrystals”.[280] They showed,
notably for 1, that many “monocrystals” were inhomogeneous and composed of several polymorphs.[280] Often,
the bulk crystal structure is used to calculate transfer integrals, which are then correlated to charge-transport characteristics.[7] However, the crystal structure at the interface with a dielectric layer can be substantially differIsr. J. Chem. 2013, 53, 1 – 27
ent.[281–289] Thin-film phases, better named substrate-induced phases, are known for 1, but also occur with other
compounds.[288,289] Their identification requires generally
tedious diffraction studies.[290–293] The occurrence of substrate-induced phases is not surprising in itself. Polymorphism is common for molecular crystals[275,276] and the
fact that it is promoted by a rigid substrate that acts as
nucleating agent is expected.[288] For crystals that are
grown independently and then deposited on a dielectric
substrate, it is also conceivable that the crystal structure
undergoes reconstruction to adapt to the new constraint
imposed by a rigid wall. Another question is to what
extent can an electrical field modify the microstructure of
the organic semiconductor at the dielectric interface? It
has been demonstrated by Cheng et al. that irreversible
structural modifications in 1 films occurred during OFET
operation.[294] Even in the absence of electric fields, films
of 1 reorganize after deposition.[295] In some cases, large
single crystals of 1 result from surface-mediated Oswlad
ripening, but with poor control of crystal position and orientation.[296] Recently, directional crystal growth methods
have received considerable attention. Growing crystals in
either a temperature gradient[252,297] or a concentration
gradient, combined with a shear field,[39,175,190,201,237,298,299]
offers the advantage of decoupling nucleation from
growth. Guided crystallization with the help of a template
or by patterning is also a method of growing importance,
and, in favorable cases, aligned crystalline domains larger
than the typical sourcedrain distance are obtained.[10,11,31,36,38,42,186,195–198,200,231,235,300,301] The most spectacular result is certainly the possibility of distorting unit cells
and reaching less stable polymorphs, as recently put forward by Bao and al.[32,33] The distortion of unit cells by
shearing is accompanied by a dramatic increase in charge
carrier mobility from 0.8 to 11 cm2 V1 s1.
3.3.3 Mesomorphism
An elegant way to avoid the problem of polymorphism is
to rely on mesomorphism, which is defined as the occurrence of intermediate, either liquid or plastic crystalline
mesophases, between the crystal and melt states.[302] Fullerene (2) represents an interesting case of a crystal plastic
phase at room temperature, that is, the centers of mass of
the molecules are positioned on a lattice, but the molecules rotate on themselves in such a way that the position
of the atoms is not correlated.[303] Nevertheless, mobility
values as high as 5–11 cm2 V1 s1 have been observed for
C60.[31a,b] It is fair to say that C60 remains a unique molecular semiconductor due to its spherical shape, allowing
three-dimensional charge transport.[68,304] Liquid-crystalline semiconductors have been abundantly studied.[305–308]
One of their main advantages is that they spontaneously
form large monodomains in thin-film geometry.[251,309,310]
Their alignment can be controlled and even patterned.[311–314] However, the order gained at long range is
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lost at short range. Liquid-crystalline semiconductors are
dramatically disordered systems, both structurally and energetically, although the disorder has a marked dynamic
character. Traps and barriers are constantly self-created
and self-healed at a characteristic timescale that matches
that of charge hopping. As a general matter of fact,
liquid-crystalline semiconductors, either composed of calamitic or discotic molecules, always perform less well
than crystalline molecular semiconductors, with generally
0.001 m 0.1 cm2 V1 s1.[315,316] Some higher mobility
values, ranging from 0.5 to 1.4 cm2 V1 s1, have also been
reported on rare occasions.[318a-c] The most ordered mesophases appearing at lower temperature display higher
charge carrier mobility; this puts forward, once more, the
negative impact of disorder on charge transport. If liquid
crystallinity is not advantageous to charge transport, it
can be instrumental for solution processing. Hanna and
Lino demonstrated that spin-coating BTBT 5, in the temperature range in which smectic phases occurred, improved the charge carrier mobility dramatically and also
reduced the spread of mobility values.[317] Liquid-crystalline phases thus appear to be advantageous for processing
molecular semiconductors.[319]
broaden the distribution of J values? Are some molecular
and crystal structures more favorable to decrease unwanted molecular motions? The general answer appears to be
yes. One very detrimental motion on charge transport, in
herringbone packing, takes place along the longer molecular axis because of the extreme dependence of J.[324] A
way to avoid large longitudinal displacement could be to
introduce bulky phenyl end groups, as recently done by
Takimiya et al. with DNTT derivatives.[46] In a sense, it
also happens for 3: longitudinal motions are largely
avoided by the bulkiness of the TIPS group in the brick
wall motif.[5,6,75] Returning to herringbone packing, calculations on tetracene dimers show that J is diminished
from about 350 meV to 0 meV for a tilt angle increasing
from 0 to 608.[89] It is common to distinguish the four different packing modes of aromatic compounds that are
schematically depicted in Figure 5.[16] Classical and cofa-
3.3.4 Molecular Motions, Packing, and Dimensionality
The extent to which dynamics limit or help charge transport is a debated question that is intimately related to the
temperature dependence of charge carrier mobility.[75,160,231,238,320] In a band-like model, phonons are detrimental to charge transport, whereas phonons promote
charge transfer in the hopping model, but phonon is
a term that encompasses a large diversity of phenomena.
Intra- and intermolecular phonons have been defined in
the Introduction. It is also good to recall that intramolecular phonons act on l, whereas intermolecular ones
impact on J.[70,71,243] How could one modify intramolecular
phonons? Deuteration appears to be the most obvious
method to try. We are not aware of any charge-transport
studies on deuterated 1, although the synthesis of the
molecule is known.[321] The adiabatic ionization potential
difference between hydrogenated and deuterated 1 is calculated to be only about 9 meV.[322] Values of charge carrier mobility above 10 cm2 V1 s1 have very recently been
measured on single crystals deuterated 4 with a vacuum
gap transistor architecture at room temperature. A maximum hole mobility of 45 cm2 V1 s1 has been reached
near 100 K. It was concluded from this work that hydrogenated and deuterated 4 behaved comparably.[224] From
these scarce data, it is tentatively concluded that deuteration is of little help to improve charge-transport characteristics. The best way to lower l remains the enlargement
of p systems.[323] This design is limited, however, by the
solubility and stability of p systems, in such a way that
a trade-off naturally appears.[9,47,48] The next question is
could how one modify intermolecular phonons that
Isr. J. Chem. 2013, 53, 1 – 27
Figure 5. Four common packing modes of aromatic compounds:
a) classical herringbone, b) cofacial herringbone, c) slipped-stacks,
and d) bricklayer, also called brick wall. Arrows indicate the preferred charge-transfer pathway, and hence, the dimensionality of
charge transport.
cial herringbone packing differ fundamentally from slipped stacks and brick wall arrangements. For the first two,
the aromatic cores lie in two sets of parallel planes with
a wide angle between them. For the last two, all aromatic
cores are located in a single set of parallel planes. The
magnitude of J depends sharply on the relative position
of the molecules within the unit cell.[5–7,47,48,243] J varies
substantially along different crystallographic directions,
engendering an anisotropy of charge transport within the
x,y plane. The anisotropy of charge carrier mobility has
been calculated and measured for several compounds, including 1,[325] 4,[24,133,326] 3,[327] and DNTT 7 (R, R’ = H).[45]
An anisotropy ratio of about two to four has been measured for the charge carrier mobility in single crystals exhibiting 2D charge transport (see Figure 5a and d). The
anisotropy ratio increases to two digits for compounds
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that crystallize in more one-dimensional packing modes,
such as slipped stacks (see Figure 5b and c).[201,327] A perfectly isotropic charge carrier mobility within the x,y
plane has not yet been reported, to the best of our knowledge. Dimensionality of charge transport cannot only be
seen from a static viewpoint.[328] J values are considerably
broadened by thermal agitation and the width of transfer
integral distribution, DJ, can be as large as J itself.[329]
In fact, the reduced dimensionality of charge transport
represents a technological obstacle. Three-dimensional
charge transport has rarely been achieved,[68,131] but is required for three-dimensional OFETs.[233,236] Nevertheless,
charge transport takes place in two dimensions in the vast
majority of OFETs. A striking example comes from monolayer OFETs.[330] For multilayered films, charges are localized in the first three molecular layers of semiconductors at the interface with the dielectrics.[177,331] Charge density is higher in the first layer and then decreases rapidly
with the number of layers. The major part of the current
is transported not in the first layer, but in the second and
third layers.[258] A likely explanation is that the electrostatic interactions with the gate dielectrics particularly
affect the charges located in the first layer.[117] The crystal
structure of a compound not only determines the magnitude of the electronic coupling, it also dictates its crystalline morphology, which can be calculated with the attachment theory reported by Hartman and Bennema.[332] Calculated and experimental crystal morphologies agree
well, as recently shown for BTBT 5.[333] Interestingly, the
best performing molecular semiconductors tend to form
plate-like crystals, as illustrated in Figure 6 for 1, 3, and
BTBT 5, although they have different packing motifs:
herringbone for 1 and 5, and brick wall for 3.[334]
3.3.5 Dielectrics, Charge Density and Doping
Dielectric layers are generally either made of a thin film
of polymers or of SiOx, upon which a self-assembled monolayer is deposited. Abundant literature has been published on the role of dielectrics on charge carrier mobility.
Several review papers have appeared and the interested
reader is directed to them for a comprehensive treatment.[34,81,82,337–339] What are the most salient facts? First,
the static dielectric constant, e, has a decisive impact on
charge carrier mobility.[146] It has been found that m / e1
for a range of e going from 1 (air) to 25 (Ta2O5).[340] The
interaction between the charges in the semiconductor and
the dipoles of the dielectrics are more intense in the first
layer and fade away rapidly in the second, third, and
fourth layers, see Section 2.5.[119] The higher charge carrier mobility values are observed for transistors with single
crystals suspended in air, also called air gap transistors.[207,341] However, Takeya et al. reported high-performance OFETs fabricated with high e dielectrics separated from the molecular semiconductors by a self-assembled monolayer. They estimated the binding energy of
a charge with dielectrics to be less than kBT. Field-effect
mobility for single crystals of 7 (R = C10H21, R’ = H)
Figure 6. Morphology of the triclinic P-1 Campbell phase of 1 (top left), the triclinic P-1 phase of 3 (top right), and the monoclinic P21/
a phase of BTBT 5, with octyl side chains (bottom) visualized with Materials Studio software,[335] using the COMPASS force field.[336]
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reached 10.7 cm2 V1 s1 and the threshold voltage (VT)
was as low as 0.2 V.[44] Second, the surface of the dielectric layer can react with charge carriers, in some cases.
The best known example is afforded by SiOH functions
on top of SiOx that react with radical anions.[342] Charge
carriers can also react with water. Thus water-repellent
dielectrics, such as fluorinated ones, are preferable.[260]
Third, the roughness of the dielectric semiconductor interface has a detrimental effect on charge carrier mobility, which is further aggravated by the low dimensionality
of molecular semiconductors.[68,81,343]
Fourth, the viscoelastic properties and molecular
weight of polymer dielectrics modify the charge transport
of polycrystalline films. This effect is due to grain size
and occurs for diverse molecular semiconductors.[147,181,344]
Now that the main findings have been presented, it is
also worth mentioning some discordant results. Baeg
et al. observed a remarkable enhancement of charge carrier mobility by a factor 1000, in a conjugated polymer,
induced by high-e fluorinated polymer dielectrics.[345] Lee
et al. reported the surprising trap healing and ultralownoise Hall effects at the surface of a single crystal of 4
due to simple contact with a liquid perfluoropolyether.[218]
The same group also modified the surface of 4 with silanes and highlighted the role of molecular steps.[346,347]
Indeed, the surface modification of a single crystal remains unexplored, but offers intriguing perspectives to
reach very high charge carrier density, that is, in the
range of 1013–14 cm2, with air gap transistors. The same
statement applies to doping by dipping single crystals of
dialkyl BTBT 5 in a solution containing a strong electron
acceptor, such as 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ).[234] However, the extent to
which the surface does not undergo a reconstruction to
incorporate F4-TCNQ in the crystal structure of dialkyl
BTBT 5[348] remains an open question. In the same vein,
electrolyte-gated, single-crystal organic transistors are another tool to examine transport in high carrier density
regime.[20,340,349] Progress comes also from practical inventions such as that of Podzorov et al., who developed
a vacuum lamination approach to fabricate single-crystal
OFETs.[350] The method, which is nondestructive, reversible, and nonperturbing, enables the dielectric in the same
device to be changed multiple times without crystal degradation. This simple vacuum lamination method paves
the way to systematic studies on the same crystal. A final
possibility is to put together two single crystals of organic
semiconductors: one is an electron donor (p type) and
the other is an electron acceptor (n type); thus charge
transfer is possible at the interface.[216] If the p- and ntype crystals are laminated on one another, the interface
remains heterogeneous and undefined, for example, one
cannot exclude the formation of voids because crystal surfaces are not completely flat at the molecular level.
Superb work has been carried out by Zhang et al., who
grew copper hexadecafluorophthalocyanine on copper
Isr. J. Chem. 2013, 53, 1 – 27
phthalocyanine to form single-crystalline pn junction
nanoribbons.[351] A key element to this success is that the
two compounds have similar lattice constants. This condition is evidently difficult to fulfill. There is evidently
a comparison to make with the donoracceptor interface
of solar cells.[352]
3.3.6 Temperature and Pressure
The temperature dependence of mobility is really at the
heart of the current debate on charge-transport mechanisms.[22,54,145,320,353] Temperature studies are particularly instructive when conducted on samples of sufficient purity
and on crystals of high quality.[21,98,252] OFETs and timeof-flight (TOF) methods have been used to probe charge
transport in two and three dimensions, respectively. When
going to subambient temperature, it is consistently observed that mobility ranging from 1 to 10 cm2 V1 s1 increases upon going to lower temperature and passes
through a maximum in the 10–100 cm2 V1 s1 range. The
temperature corresponding to the maximum of mobility
varies largely from about 30 to 200 K.[98,203,252] Interestingly, comparable thermal behavior takes place for thermal
conductivity measured in bulk crystals of 4, with a maximum value at low temperature, occurring at around
10 K.[215] One noticeable exception is single crystals of
DNTT 7 (R, R’ = H), which exhibit a more complicated
charge carrier mobility dependence on temperature, in
the 200–300 K range, that is also sample specific. These
results are accompanied by X-ray diffraction characterization, demonstrating the single-crystal quality of the samples.[45] Upon increasing the temperature from ambient
values to about 580 K, DNTT 7 (R = phenyl, R’ = H)
demonstrates a fairly constant charge carrier mobility.
This interesting behavior for medical applications requiring sterilization can be attributed to the high rigidity of
this molecule.[238] DNT-V 9 shows a similar quasi-constant
mobility, but up to 400–450 K.[49] When discussing temperature effects on charge carrier mobility, one must keep in
mind that transistors are composed of several materials
with different thermal expansion coefficients, a. The situation is even further complicated for single crystals of
molecular semiconductors that have different thermal expansion coefficients along the a, b, and c directions, aa ¼
6
6 ac. It is anticipated that large temperature variations
ab ¼
are likely to cause stress inside materials and eventually
force them to delaminate at interfaces. We are not aware
of many reports on the thermal and mechanical properties of single crystals of molecular semiconductors, except
for 3 and 4.[193,217] Note that the thermal expansion of the
crystal lattice has been found to be the main factor responsible for the bandwidth narrowing of 1 and 4.[354]
Charge carrier mobility is a function of temperature, but
how does it depend on pressure? In the absence of phase
transitions, higher pressures force molecules to come
closer and J increases. Does it reflect on the m values?
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Rang et al. answered this question with a pressure study
on single-crystal OFETs of 4.[355] The pressure has been
increased up to 0.52 GPa (5.2 108 N m2, 5100 atm), but
the intermolecular distances is only decreased by about
1.5% and the mobility increases linearly from 6 to
10 cm2 V1 s1. The effect is negligibly small. Note, however, that Bard and Liu observed a pressure-induced insulatorconductor transition in a photoconducting organic
liquid-crystal film.[356]
3.3.7 Electrodes, Fermi Level, Ionization Potential, and Injection
Barrier
To record field-effect mobility, the electrical resistance of
contacts (Rcontact) between metal electrodes and the molecular semiconductor must be much lower than the channel resistance (Rchannel), which scales with the channel
length. Effectively, field-effect mobility scales with the
channel length (L), as demonstrated by Klauk et al. for
thin films of 1.[357] When the condition Rcontact ! Rchannel is
verified, contacts are qualified as “ohmic”.[2] Note that
Rcontact = Rsource + Rdrain, with Rsource and Rdrain being the contact resistance of the source and the drain, respectively,
and Rsource Rdrain. Rcontact varies substantially for gold electrodes, that is, from 2 103 to 106 Wcm, whereas it changes
by only a factor 2 for nickel electrodes, that is, from 500
to 1000 Wcm.[358] In direct relation to the title of this
paper, it must be stressed that high-m semiconductors require low Rcontact. Experimental evidence of low Rcontact is
a low Vg value to switch on the transistor. In the case of
hole transport, it is commonly written that the Fermi
level (EF) of the metal electrodes must match the ionization potential (IP) of the molecular semiconductors.[359]
This statement appears correct, at first glance, but it deserves further comment. IP is often estimated from solution measurements of the first oxidation potential (Eox),
as recently discussed by Bazan et al.[360] The underlying
hypothesis for this estimation is that the energetics of the
polarization process around a positive charge in the solid
state is almost equal for all molecular semiconductors,
that is P + = IPsolid stateIPgas phase constant, which simply
represents the difference in IP for a molecule in the solid
state (IPsolid state), surrounded by neighbors, and for an isolated molecule in the gas phase (IPgas phase).[114,121,361,362] This
hypothesis neglects the effect of solid-state arrangement
and is not experimentally verified for crystalline semiconductors, as shown by the values of P + for 1 (1.73 eV) and
3 (0.44 eV) that are radically different.[363,364] Moreover,
Koch et al. demonstrated that IP varied by up to 0.6 eV
as a function of molecular orientation.[365] It is also worth
mentioning that the electronic structure of the p systems
in direct contact with the metal surface can substantially
be modified too, but it depends very much on the molecular structure of the p systems and on the metal. Pentacene (1), like the majority of organic semiconductors, retains its intrinsic electronic characteristics, whereas 6,13Isr. J. Chem. 2013, 53, 1 – 27
pentacenequinone (a common impurity of 1) does not.
The latter undergoes surface-induced aromatic stabilization with a substantial distortion of its bond lengths.[366]
Even in the absence of such an extreme effect, the work
function (f) of a clean metal surface can be dramatically
altered by the adsorption of p systems. The potential barrier is modified by two mechanisms: the formation of
local dipoles associated with chemisorption of p systems
and the Pauli repulsion between metal electrons and
those of p systems. The latter is effective in the case of
weak metalorganic coupling.[367] It must be stressed that
energetic misalignment of a few meV can modify contact
resistance.[368] However, charge injection and collection at
source and drain electrodes are only partially determined
by the presence of a potential barrier. Other factors, such
as structural disorder near the contacts and wetting effects, must also be taken into account.[2,369] Several groups
have worked on the modification of electrode surfaces to
understand and improve charge injection. A highlight is
given by the work of Biscarini et al., who modified gold
electrodes with alkanethiols of increasing length. The
field-effect mobility of films of 1 fluctuates with an odd
even effect up to octanethiol. For longer alkanethiols, m
decays exponentially with an inverse decay length of
0.6 1.[370] The interface energetics of self-assembled
monolayers on metals has been reviewed by Brdas
et al.[359] Recently, Samori et al. fabricated OFETs with
source and drain modified with dodecanethiol and hexanethiol, respectively. Nonsymmetric source and drain
electrodes are evidently advantageous for ambipolar
transport.[371] The same group demonstrated that charge
injection could be modulated by photochromic self-assembled monolayers chemisorbed on gold electrodes.[372]
As a matter of fact, the origin of contact resistance remains an unsolved question in organic electronics. It is
fair to say that the problem is complex and is intimately
linked to the structure of the metalorganic interface,
which is difficult to probe experimentally. In this regard,
bottom- and top-contact transistors differ substantially.[373]
For bottom-contact OFETs, where a triple interface between metal, semiconductor, and dielectric is present, the
results of Rogers et al. show that the barrier to charge injection also depends on the dielectric layer.[374] The case
of top-contact OFETs is equally interesting because it
demonstrates that the reduced dimensionality of charge
transport of molecular crystals is detrimental to high
field-effect mobility. Kloc et al. put forward that the thinner single crystals exhibited much higher conductivity.[180]
3.3.8 Is Charge Carrier Mobility a Material Property?
It can be concluded from this section devoted to materials
that there is a general consensus on what are the best-performing molecular semiconductors for charge transport.
Many compounds have been synthesized and their charge
transport characterized but few exhibit m 10 cm2 V1 s1.
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Beforehand, it is nearly impossible to identify among
novel molecular structures which one will give rise to
high mobility values. Through observations, it is possible
to rationalize charge-transport properties based on molecular and crystal structures. However, charge carrier
mobility depends on many extrinsic parameters. With the
fantastic amount of work that has been engaged in the
field of organic electronics, one could certainly hope that
soon intrinsic charge-transport properties will be measured that will allow discrimination on the basis of molecular arguments.
4 Measurements
4.1 Essential Considerations
OFETs have been the topic of several excellent review
papers[14,17,21,34,79,81,82,87,91] and books.[1–4] The interested
reader is directed to them for elaborated discussions on
fabrication methods, device architectures, working principles, and currentvoltage characteristics. One obvious
conclusion from this large body of literature is that
charge carrier mobility depends enormously on the devices that are used to measure it and also on the way they
are operated. It is pertinent to mention in this context
that a strong kinetic effect has recently been reported for
the measurements of different OFETs. A charge carrier
mobility varying by a factor as large as 20 has been recorded for a Vg sweep rate ranging from 0.1 to 10 V s1;
Vg is the gate voltage.[43] Thus, the question of the title
makes sense, only if charge carrier mobility values are
measured in a reliable and reproducible manner.[54] On
one hand, absolute values must be trustable to understand charge-transport physics from first principles. On
the other hand, values must be comparable within a given
set of experimental conditions to determine accurately
the properties of the materials and to draw reliable structureproperty relationships upon which the design of new
materials is based. As highlighted in previous sections,
field-effect mobility is the most commonly used parameter to evaluate the electrical performance of a new organic semiconductor. As a direct answer to the high performance required for electronic organic circuitries, academic and industrial researchers have begun the quest for
the highest mobility values, leading to an outstanding
seven orders of magnitude improvement of the fieldeffect mobility during recent decades. Actually, most of
the reported mobility values are extracted from OFET
measurements using standard Schockley equations for the
linear and saturation regimes:
Id ¼
Id and Id-sat are the current between source and drain in
the linear and saturation regimes, respectively; W is the
channel width; C is the capacitance; Vd is the voltage between source and drain; and Vth is the threshold voltage
applied between the source and gate to switch on the
transistor.[2,82,375]
Such extractions require, however, a linear fit of the
gate voltage dependence of the current in the linear
regime or of the square root of the current in the saturation regime. Researchers should be cautious about reporting high mobility values when nonlinearities show up.
The question “how should we report or treat high mobility in the case of nonideality?” is a very difficult one that
almost any researcher in this field has faced, or is going
to face, at some point. The answer is even more difficult
to formulate because of the constant evolution of organic
electronics; this presents a large panel of device architectures, dielectrics, and electrodes.[86,91] In such a vast environment, free of any standard protocols of extraction, scientists should be self-critical and only report high mobility values if their devices pass different requirements: 1)
The absence of a gate voltage sweeping rate dependence
of the mobility, generally assigned to a dispersive transport and charge trapping in the organic semiconductor or
at the interface.[43] It is also worth mentioning that a dispersive transport could also be highlighted by a temporal
decrease of the drain current during bias stress measurements, as well as by transfer curve hystereses, exhibiting
a higher on current during the forward sweep compared
with the backward one.[43,91] 2) A near-linear fit of the
gate voltage dependence of the current in the linear
regime or of the square root of the current in the saturation regime and a consistence of the mobility value extracted from both regimes. Reporting mobility values in
both regimes should be standard.[49,54,350] 3) The extracted
mobility does not exist as a sharp peak over a small gate
voltage range in the subthreshold regime (at small negative gate voltage). This effect, largely observed on devices
using SiO2 as the dielectric, can be associated to a superlinear increase of the conductivity due to the rapid opening of the Schottky contacts. The claim of high mobility
should always be demonstrated by a plot of the mobility
versus the gate voltage, highlighting the presence of a plateau regime corresponding to the linear transconductance
region, where the transistor is in the ohmic regime.[54,350]
This section does not intend to question the fact that
a broad range of organic semiconductors actually present
mobility values higher than amorphous silicon. However,
we believe that mobility extraction requires caution in
the presence of nonideality, especially when claiming high
mobility values.
W
mC Vg Vth Vd
L
Idsat ¼
W
m C Vg Vth 2
2L sat
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4.2 Other Methods to Measure Charge Carrier Mobility and
Correlation with Spectroscopic Studies
Charge carrier mobility has been measured, in bulk, by
TOF and space charge limited current (SCLC).[252,98,376]
One might argue that charge carrier mobility measured in
three dimensions and field-effect mobility measured in
two dimensions are not directly comparable because of
the higher charge density intrinsic to OFETs and because
of the influence of the dielectric layer. It is therefore important to have other ways to independently measure
charge carrier mobility. The Hall effect offers an alternative method, with the additional advantage that it is possible to measure mobility on the same devices. Importantly,
Hall mobility values corroborate field-effect mobility
values rather well.[54,124,218,216,377,378] The highest Hall mobility value has been obtained for single crystals of 4 and is
about 18 cm2 V1 s1.[379] This value is consistent with previous measurements of the mobility in OFETs of 4 along
the b axis.[203,380] One final technique deserves some attention: pulse-radiolysis time-resolved microwave conductivity (PR-TRMC) has been very instrumental to benchmark the performances of organic semiconductors.[92,381]
Recently, the group of Seki has developed a new technique called field-induced time-resolved microwave conductivity (FI-TRMC) for evaluating charge carrier mobility at the semiconductor/dielectrics interface. Interestingly,
FI-TRMC also clarifies the contribution of hole and electron conduction.[382] This method holds great promises for
the rapid screening of a large number of semiconductor
dielectric pairs. Charge carriers are either holes (radical
cations) or electrons (radical anions). In both cases, unpaired electrons are present that give rise to specific spectral signatures. Charges in molecular semiconductors have
characteristic charge-induced optical absorptions that reflect the degree of polaronic reorganization associated
with their formation.[213] Recent studies by Sirringhaus
et al. showed that charge carriers were not mesoscopically
extended over a large number of molecules, but only over
a small number of them.[124,160] The question of charge delocalization is particularly important to explain chargetransport mechanism[54,145,353] and ultimately the ultimate
charge carrier mobility that could reasonably be expected
in molecular semiconductors. Unpaired electrons are also
detectable by electron spin resonance.[204,229] Using this
method, no evidence of a prominent polaronic effect has
been detected in single crystals of 4. It was concluded
that the polaron binding energy in 4 should be inferior to
26 meV at room temperature.[204] Generally, the overabundance of field-effect mobility values reported in the literature contrasts with the scarcity of Hall mobility measurements that allow them to be cross-checked. This conclusion can be extended to spectroscopic studies.
Isr. J. Chem. 2013, 53, 1 – 27
5 Conclusions and Perspectives
The most honest answer to the question: What currently
limits charge carrier mobility in crystals of molecular
semiconductors? is “many things”. Charge carrier mobility is not a scalar, but a function that depends on diverse
parameters: molecular structure, crystal packing, polymorphism, mesomorphism, purity, disorder, defects, traps,
dielectrics, transistor architecture, charge density, packing,
time, and temperature. Together, they ultimately determine mobility values. One might argue that these parameters do not all have the same importance. It is likely that
the concentration of defects and their energy distribution
determine the order of magnitude of the ultimate values
of mobility, whereas other secondary factors modulate it.
It is important to keep in mind that charge carrier mobility is one of the characteristics of a transistor that must be
reported with others to be meaningful, in particular, on/
off ratio and threshold voltage. Charge carrier mobility
measured, on single crystals, in OFETs, for charge travelling at two dimensions, ranges from 1 to 20 cm2 V1 s1, in
the best cases, at room temperature and applying reproducibility criteria. Upon lowering the temperature, mobility increases to reach a maximum value between 10 and
100 cm2 V1 s1. Reliable measurements of charge transport in three dimensions by photoconductivity methods
give comparable orders of magnitude and show similar
behavior with temperature. Are molecular semiconductors definitively limited to values ranging between 1 and
20 cm2 V1 s1, at room temperature or are higher values
available? Current theories do not indicate any intrinsic
limitations to charge carrier mobility that result from
a compromise between thermal agitation, inducing energetic disorder, and electronic coupling of adjacent molecules. Thus, the value of 20 cm2 V1 s1 is not likely to be
a limit. We see three ways of improvement. First, crystal
engineering could lead to shorter intermolecular distances
and higher electronic coupling. Second, surface modifications remain unexplored for single crystals and offer the
perspective of reaching trap-free transport. Besides achieving higher values of mobility, it is also indispensable to
gain a more fundamental understanding of physical processes occurring during charge transport. Third, charge injection and collection at metalsemiconductor contacts
must be improved. To this end, materials chemists have
access to a large number of molecular structures that
could be engineered to facilitate charge-transport electron transfer.
Acknowledgements
This work has received funding from the Belgian National Fund for Scientific Research (FNRS-Research fellow
PhD grant for G. S. and project BTBT no. 2.4565.11),
from a concerted research action of the French Commun-
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ity of Belgium (ARC project no. 20061). Y. G. benefits
from a mandate of Francqui Research Professor. In addition, the work in Mons was supported by the European
Commission/Rgion Wallonne (FEDERSmartfilm RF
project), the Interuniversity Attraction Pole program of
the Belgian Federal Science Policy Office (PAI 7/05), and
Programme dExcellence de la Rgion Wallonne (OPTI2
MAT project). The authors are grateful to D. Beljonne, J.
Cornil, A. Morpugo, V. Podzorov, J.-i. Hanna and J. E.
Anthony for fruitful discussions.
References
[1] Organic Electronics: Materials, Manufacturing, and Applications (Ed.: H. Klauk), Wiley-VCH, Weinheim, 2006.
[2] Organic Field-Effect Transistors (Eds.: Z. Bao, J. Locklin),
CRC Press, Boca Raton, 2007.
[3] Organic Electronics II (Ed.: H. Klauk), Wiley-VCH, Weinheim, 2012.
[4] Organic Electronics, Emerging Concepts and Technology
(Eds.: F. Cicoira, C. Santato), Wiley-VCH, Weinheim,
2013.
[5] J. E. Anthony, Chem. Rev. 2006, 106, 5028 – 5048.
[6] J. E. Anthony, Angew. Chem. Int. Ed. 2008, 47, 452 – 483.
[7] K. Takimiya, S. Shinamua, I. Osaka, E. Miyazaki, Adv.
Mater. 2011, 23, 4347 – 4370.
[8] C. Wang, H. Dong, W. Hu, D. Zhu, Chem. Rev. 2012, 112,
2208 – 2267.
[9] M. Watanabe, K.-Y. Chen, Y. J. Chang, T. J. Chow, Acc.
Chem. Res. 2013, 46, 1606 – 1615. >
[10] J. A. Lim, H. S. Lee, W. H. Lee, K. Cho, Adv. Funct. Mater.
2009, 19, 1515 – 1525.
[11] S. Liu, W. M. Wang, A. L. Briseno, S. C. B. Mannsfeld, Z.
Bao, Adv. Mater. 2009, 21, 1217 – 1232.
[12] A. A. Virkar, S. Mannsfeld, Z. Bao, N. Stingelin, Adv.
Mater. 2010, 22, 3857 – 3875.
[13] R. Li, W. Hu, Y. Liu, D. Zhu, Acc. Chem. Res. 2010, 43,
529 – 540. >
[14] M. Mas-Torrent, C. Rovira, Chem. Rev. 2011, 111, 4833 –
4856.
[15] G. De Luca, W. Pisula, D. Credgington, E. Treossi, O. Fenwick, G. M. Lazzerini, R. Dabirian, E. Orgiu, A. Liscio, V.
Palermo, K. Mllen, F. Cacialli, P. Samor, Adv. Funct.
Mater. 2011, 21, 1279 – 1295.
[16] H. Dong, X. Fu, J. Liu, Z. Wang, W. Hu, Adv. Mater. 2013,
25, 6158 – 6183.
[17] V. Podzorov, MRS Bull 2013, 38, 15 – 24.
[18] H. Jiang, C. Kloc, MRS Bull. 2013, 38, 28 – 33.
[19] H. Li, G. Giri, J. B.-H. Tok, Z. Bao, MRS Bull. 2013, 38,
34 – 42.
[20] W. Xie, C. D. Frisbie, MRS Bull. 2013, 38, 43 – 50.
[21] I. Gutirrez Lezama, A. F. Morpugo, MRS Bull. 2013, 38,
51 – 56.
[22] V. Coropceanu, Y. Li, Y. Yi, L. Zhu, J.-L. Brdas, MRS
Bull. 2013, 38, 57 – 64.
[23] S. Bergantin, M. Moret, Cryst. Growth Des. 2012, 12,
6035 – 6041.
[24] C. Reese, Z. Bao, Mater. Today 2007, 10, 20 – 27.
[25] A. L. Briseno, S. C. B. Mannsfeld, S. A. Jenekhe, Z. Bao,
Y. Xia, Mater. Today 2008, 11, 38 – 47.
Isr. J. Chem. 2013, 53, 1 – 27
[26] O. D. Jurchescu, B. J. van Wees, T. T. M. Palstra, Adv.
Mater. 2007, 19, 688 – 692.
[27] Y. Takeyama, S. Ono, Y. Matsumoto, Appl. Phys. Lett.
2012, 101, 083303.
[28] K. Itaka, M. Yamashiro, J. Yamaguchi, M. Haemori, S. Yaginuma, Y. Matsumoto, M. Kondo, H. Koinuma, Adv.
Mater. 2006, 18, 1713 – 1716.
[29] T. D. Anthopoulos, B. Singh, N. Marjanovic, N. S. Sariciftci,
A. Montaigne, A. M. Ramil, H. Sitter, M. Colle, D. M.
de Leeuw, Appl. Phys. Lett. 2006, 89, 213504.
[30] X.-H. Zhang, B. Kippelen, J. Appl. Phys. 2008, 104,
104504.
[31] a) H. Li, B. C. K. Tee, J. J. Cha, Y. Cui, J. W. Chung, S. Y.
Lee, Z. Bao, J. Am. Chem. Soc. 2012, 134, 2760 – 2765;
b) X.-H. Zhang, B. Domercq, B. Kippelen, Appl. Phys.
Lett. 2007, 91, 92114.
[32] G. Giri, E. Verploegen, S. Mannsfeld, S. Atahan-Evrenk,
D. H. Kim, S. Y. Lee, H. A. Becerril, A. Aspuru-Guzik,
M. F. Toney, Z. Bao, Nature 2011, 480, 504 – 508.
[33] Y. Diao, B. C.-K. Tee, G. Giri, J. Xu, D. Hwam Kim, H. A.
Becerril, R. M. Stoltenberg, T. Hoon Lee, G. Xue, S. C. B.
Mannsfeld, Z. Bao, Nat. Mater. 2013, 12, 665 – 672.
[34] D. Braga, G. Horowitz, Adv. Mater. 2009, 23, 1473 – 1486.
[35] J. Takeya, M. Yamagishi, Y. Tominari, R. Hirahara, Y. Nakazawa, T. Nishikawa, T. Kawase, T. Shimoda, S. Ogawa,
Appl. Phys. Lett. 2007, 90, 102120.
[36] T. Uemura, Y. Hirose, M. Uno, K. Takimiya, J. Takeya,
Appl. Phys. Express 2009, 2, 111501.
[37] P. S. Jo, A. Vailionis, Y. M. Park, A. Salleo, Adv. Mater.
2012, 24, 3269 – 3274.
[38] H. Minemawari, T. Yamada, H. Matsui, J. Tsutsumi, S.
Haas, R. Chiba, R. Kumai, T. Hasegawa, Nature 2011, 475,
364 – 367.
[39] Y. Yuan, G. Giri, A. L. Ayzner, A. P. Zoombelt, S. C. B.
Mannsfeld, J. Chen, D. Nordlund, M. F. Toney, J. Huang,
Z. Bao, Nat. Commun. 2013, 4, 3005.
[40] A. Y. Amin, A. Khassanov, K. Reuter, T. Meyer-Friedrischsen, M. Halik, J. Am. Chem. Soc. 2012, 134, 16548 –
16550.
[41] M.-J. Kang, I. Doi, H. Mori, E. Miyazaki, K. Takimiya, M.
Ikeda, H. Kuwabara, Adv. Mater. 2011, 23, 1222 – 1225.
[42] K. Nakayama, Y. Hirose, J. Soeda, M. Yoshizumi, T.
Uemura, M. Uno, W. Li, M. J. Kang, M. Yamagishi, Y.
Okada, E. Miyazaki, Y. Nakazawa, A. Nakao, K. Takimiya,
J. Takeya, Adv. Mater. 2011, 23, 1626 – 1629.
[43] Y. Chen, B. Lee, H. T. Yi, S. S. Lee, M. M. Payne, S. Pola,
C.-H. Kuo, Y.-L. Loo, J. E. Anthony, Y. T. Tao, V. Podzorov, Phys. Chem. Chem. Phys. 2012, 14, 14142 – 14151.
[44] W. Ou-Yang, T. Uemura, K. Miyake, S. Onish, T. Kato, M.
Katayama, M. Kang, K. Takimiya, M. Ikeda, H. Kuwabara,
M. Hamada, J. Takeya, Appl. Phys. Lett. 2012, 101, 223304.
[45] W. Xie, K. Willa, Y. Wu, R. Husermann, K. Takimiya, B.
Batlogg, C. D. Frisbie, Adv. Mater. 2013, 25, 3478 – 3484.
[46] M.-J. Kang, E. Miyazaki, I. Osaka, K. Takimiya, A. Nakao,
ACS Appl. Mater. Interfaces 2013, 5, 2331 – 2336.
[47] K. Niimi, S. Shinamura, I. Osaka, E. Miyazaki, K. Takimiya, J. Am. Chem. Soc. 2011, 133, 8732 – 8739.
[48] A. N. Sokolov, S. Atahan-Evrenk, R. Mondal, H. B. Akkerman, R. S. Snchez-Carrera, S. Granados-Focil, J. Schrier,
S. C. B. Mannsfeld, Arjan P. Zoombelt, Z. Bao, A. AspuruGuzik, Nat. Commun. 2011, 2, 437 – 445.
[49] T. Okamoto, C. Mitsui, M. Yamagishi, K. Nakahara, J.
Soeda, Y. Hirose, K. Miwa, H. Sato, A. Yamano, T. Mat-
2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.ijc.wiley-vch.de
&19&
These are not the final page numbers! ÞÞ
Review
[50]
[51]
[52]
[53]
[54]
[55]
[56]
[57]
[58]
[59]
[60]
[61]
[62]
[63]
[64]
[65]
[66]
[67]
[68]
[69]
[70]
[71]
[72]
[73]
[74]
[75]
[76]
sushita, T. Uemura, J. Takeya, Adv. Mater. 2013, 25, 6392 –
6397.
Y. Takahashi, T. Hasegawa, S. Horiuchi, R. Kumai, Y.
Tokura, G. Saito, Chem. Mater. 2007, 19, 6382 – 6384.
L. Li, Q. Tang, H. Li, X. Yang, W. Hu, Y. Song, Z. Shuai,
W. Xu, Y. Liu, D. Zhu, Adv. Mater. 2007, 19, 2613 – 2617.
N. Kurihara, A. Yao, M. Sunagawa, Y. Ikeda, K. Terai, H.
Kondo, M. Saito, H. Ikeda, H. Nakamura, Jpn. J. Appl.
Phys. 2013, 52, 05DC11.
Y. S. Yang, T. Yasuda, H. Kakizoe, H. Mieno, H. Kino, Y.
Tateyama, C. Adachi, Chem. Commun. 2013, 49, 6483 –
6485.
N. A. Minder, S. Ono, Z. Chen, A. Facchetti, A. F. Morpugo, Adv. Mater. 2012, 24, 503 – 508.
E. J. Meijer, D. M. de Leeuw, S. Setayesh, E. Van Veenendaal, B.-H. Huisman, P. W. M. Blom, J. C. Hummelen, U.
Scherf, T. M. Klapwijk, Nat. Mater. 2003, 2, 678 – 682.
V. Coropceanu, J. Cornil, D. A. da Silva Filho, Y. Olivier,
R. Silbey, J.-L. Brdas, Chem. Rev. 2007, 107, 926 – 952.
V. Umansky, M. Heiblum, Y. Levinson, J. Smet, J. Nbler,
M. Dolev, J. Cryst. Growth 2009, 311, 1658 – 1661.
T. Drkop, S. A. Getty, E. Cobas, M. S. Fuhrer, Nano Lett.
2004, 4, 35 – 39.
L. Hu, D. S. Hecht, G. Grner, Nano Lett. 2004, 4, 2513 –
2517.
A. K. Geim, K. S. Novoselov, Nat. Mater. 2007, 6, 183 – 191.
K. I. Bolotin, K. J. Sikes, Z. Jiang, M. Klima, G. Fudenberger, J. Hone, P. Kim, H. L. Stormer, Solid State
Commun. 2008, 146, 351 – 355.
D. K. Ferry, Semiconductor Transport, Taylor & Francis,
London, 2000.
R. Martins, E. Fortunato, P. Barquinha, L. Pereira, Transparent Oxide Electronics: From Materials to Devices,
Wiley-VCH, Weinheim, 2012.
K. K. Banger, Y. Yamashita, K. Mori, R. L. Peterson, T.
Leedham, J. Rickard, H. Sirringhaus, Nat. Mater. 2011, 10,
45 – 50.
E. Fortunato, P. Barquinha, R. Martins, Adv. Mater. 2012,
24, 2945 – 2986.
S. R. Thomas, P. Pattanasattayavong, T. D. Anthopoulos,
Chem. Soc. Rev. 2013, 42, 6910 – 6923.
J. N. Israelachvili, Intermolecular and Surface Forces, 3rd
Ed., Academic Press, San Diego, 2011.
J. Skabara, J.-B. Arlin, Y. H. Geerts, Adv. Mater. 2013, 25,
1948 – 1954.
N. Martinelli, J. Id, R. S. Sanchez-Carrera, V. Coropceanu,
J. L. Brdas, L. Ducasse, F. Castet, J. Cornil, D. Beljonne,
J. Phys. Chem. C 2010, 114, 20678 – 20685.
V. Coropceanu, R. S. Snchez-Carrera, P. Paramonov,
G. M. Day, J.-L. Brdas, J. Phys. Chem. C 2009, 113, 4679 –
4686.
R. S. Snchez-Carrera, P. Paramonov, G. M. Day, V. Coropceanu, J.-L. Brdas, J. Am. Chem. Soc. 2010, 132, 14437 –
14446.
Y. Olivier, L. Muccioli, V. Lemaur, Y. H. Geerts, C. Zannoni, J. Cornil, J. Phys. Chem. B 2009, 113, 14102 – 14111.
D. P. McMahon, A. Troisi, ChemPhysChem, 2010, 11,
2067 – 2074.
T. Vehoff, Y. S. Chung, K. Johnston, A. Troisi, D. Y. Yoon,
D. Andrienko, J. Phys. Chem. C 2010, 114, 10592 – 10597.
A. S. Eggeman, S. Illig, A. Troisi, H. Sirringhaus, P. A.
Midgley, Nat. Mater. 2013, 12, 1045 – 1049.
K. Kudo, M. Yamashita, T. Moriizumi, Jpn. J. Appl. Phys.
1984, 23, L30.
Isr. J. Chem. 2013, 53, 1 – 27
[77] A. Tsumura, H. Koezuka, T. Ando, Appl. Phys. Lett. 1986,
49, 1210 – 1212.
[78] J. Mei, Y. Diao, A. L. Appleton, L. Fang, Z. Bao, J. Am.
Chem. Soc. 2013, 135, 6724 – 6746.
[79] C. D. Dimitrakopoulos, P. R. Malenfant, Adv. Mater. 2002,
14, 99 – 117.
[80] Y. Sun, Y. Liu, D. Zhu, J. Mater. Chem. 2005, 15, 53 – 65.
[81] H. Sirringhaus, Adv. Mater. 2005, 17, 2411 – 2426.
[82] J. Zaumseil, H. Sirringhaus, Chem. Rev. 2007, 107, 1296 –
1323.
[83] M. Mas-Torrent, C. Rovira, Chem. Soc. Rev. 2008, 37, 827 –
838.
[84] A. Facchetti, Mater. Today 2007, 10, 28 – 37.
[85] Y. Shirota, H. Kageyama, Chem. Rev. 2007, 107, 953 – 1010.
[86] A. R. Murphy, J. M. J. Frchet, Chem. Rev. 2007, 107,
1066 – 1096.
[87] H. Sirringhaus, Adv. Mater. 2009, 21, 3859 – 3873.
[88] H. Dong, C. Wang, W. Hu, Chem. Commun. 2010, 46,
5211 – 5222.
[89] L. Wang, G. Nan, X. Yang, Q. Peng, Q. Li, Z. Shuai,
Chem. Soc. Rev. 2010, 39, 423 – 434.
[90] A. Operamolla, G. M. Farinola, Eur. J. Org. Chem. 2011,
423 – 450.
[91] H. Sirringhaus, Adv. Mater. 2014, 26, 1319–1335.
[92] F. Grozema, L. D. Siebbeles, J. Phys. Chem. Lett. 2011, 2,
2951 – 2958.
[93] S. Holliday, J. E. Donaghey, I. McCulloch, Chem. Mater.
2014, 26, 647–663.
[94] D. A. Bardwell, C. S. Adjiman, Y. A. Arnautova, E. Bartashevich, S. X. M. Boerrigter, D. E. Braun, A. J. CruzCabeza, G. M. Day, R. G. Della Valle, G. R. Desiraju, B. P.
van Eijck, J. C. Facelli, M. B. Ferraro, D. Grillo, M. Habgood, D. W. M. Hofmann, F. Hofmann, K. V. J. Jose, P. G.
Karamertzanis, A. V. Kazantsev, J. Kendrick, L. N. Kuleshova, F. J. J. Leusen, A. V. Maleev, A. J. Misquitta, S. Mohamed, R. J. Needs, M. A. Neumann, D. Nikylov, A. M.
Orendt, R. Pal, C. C. Pantelides, C. J. Pickard, L. S. Price,
S. L. Price, H. A. Scheraga, J. van de Streek, T. S. Thakur,
S. Tiwari, E. Venuti, I. K. Zhitkov, Acta Cryst. 2011, B67,
535 – 551.
[95] R. G. Kepler, Phys. Rev. 1960, 119, 1226 – 1229.
[96] W. Warta, N. Karl, Phys. Rev. B 1985, 32, 1172 – 1182.
[97] O. D. Jurchescu, J. Baas, T. T. M. Palstra, Appl. Phys. Lett.
2004, 84, 3061 – 3063.
[98] N. Karl, K.-H. Kraft, J. Marktanner, M. Mnch, F. Schatz,
R. Stehle, H.-M. Uhde, J. Vac. Sci. Technol. 1999, A17,
2318 – 2328.
[99] M. Mas-Torrent, P. Hadley, S. T. Bromley, N. Crivillers, J.
Veciana, C. Rovira, Appl. Phys. Lett. 2005, 86, 012110.
[100] X. Yang, Q. Li, Z. Shuai, Nanotechnology 2007, 18, 424029.
[101] E. F. Valeev, V. Coropceanu, D. A. da Silva, S. Salman,
J. L. Brdas, J. Am. Chem. Soc. 2006, 128, 9882 – 9886.
[102] L. Viani, Y. Olivier, S. Athanasopoulos, D. A. da Silva Filho, J. Hulliger, J. L. Brdas, J. Gierschner, J. Cornil, ChemPhysChem 2010, 11, 1062 – 1068. >
[103] J. L. Brdas, J. P. Calbert, D. A. da Silva Filho, J. Cornil,
Proc. Natl. Acad. Sci. USA 2002, 99, 5804 – 5809.
[104] J. L. Brdas, D. Beljonne, V. Coropceanu, J. Cornil, Chem.
Rev. 2004, 104, 4971 – 5004.
[105] V. Lemaur, D. A. da Silva Filho, V. Coropceanu, M. Lehmann, Y. Geerts, J. Piris, M. G. Debije, A. M. van de
Craats, K. Senthilkumar, L. D. A. Siebbeles, J. M. Warman,
J. L. Brdas, J. Cornil, J. Am. Chem. Soc. 2004, 126, 3271 –
3279.
2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.ijc.wiley-vch.de
&20&
These are not the final page numbers! ÞÞ
Review
[106] V. Lemaur, S. Bouzakraoui, Y. Olivier, P. Brocorens, C.
Burhin, J. El Beghdadi, A. Martin-Hoyas, A. Jonas, D. A.
Serban, A. Vlad, N. Boucher, J. Leroy, M. Sferrazza, S.
Melinte, S. Sergeev, Y. Geerts, R. Lazzaroni, J. Cornil, B.
Nysten, J. Phys. Chem. C 2010, 114, 4617 – 4627.
[107] D. P. McMahon, A. Troisi, J. Phys. Chem. Lett. 2010, 1,
941 – 946.
[108] V. Coropceanu, M. Malagoli, D. A. da Silva Filho, N. E.
Gruhn, T. G. Bill, J. L. Brdas, Phys. Rev. Lett. 2002, 89,
275503.
[109] V. Lemaur, M. C. Steel, D. Beljonne, J. L. Brdas, J. Cornil,
J. Am. Chem. Soc. 2005, 127, 6077 – 6086.
[110] R. A. Marcus, Rev. Mod. Phys. 1993, 65, 599 – 610.
[111] J. Jortner, J. Chem. Phys. 1976, 64, 4860 – 4867.
[112] G. J. Nan, X. D. Yang, L. J. Wang, Z. Shuai, Y. Zhao, Phys.
Rev. B 2009, 79, 115203.
[113] E. Silinsh, V. Capek, Organic Molecular Crystals: Interaction, Localization, and Transport Phenomena, American
Institute of Physics, New York, 1994.
[114] J. Cornil, S. Verlaak, N. Martinelli, A. Mityashin, Y. Olivier, T. Van Regemorter, L. Muccioli, C. Zannoni, F. Castet,
D. Beljonne, P. Heremans, Acc. Chem. Res. 2013, 46, 434 –
443.
[115] J. Cottaar, P. A. Bobbert, Phys. Rev. B 2006, 74, 115204.
[116] M. C. J. M. Vissenberg, M. Matters, Phys. Rev. B 1998, 57,
12964.
[117] J. J. Brondijk, W. S. C. Roelofs, S. G. J. Mathijssen, A.
Shehu, T. Cramer, F. Biscarini, P. W. M. Blom, D. M. de Leeuw, Phys. Rev. Lett. 2012, 109, 056601.
[118] A. J. Kronemeijer, V. Pecunia, D. Venkateshvaran, M. Nikolka, A. Sadhanala, J. Moriarty, M. Szumilo, H. Sirringhaus, Adv. Mater. 2014, 26, 728–733.
[119] N. G. Martinelli, M. Savini, L. Muccioli, Y. Olivier, F.
Castet, C. Zannoni, D. Beljonne, J. Cornil, Adv. Funct.
Mater. 2009, 19, 3254 – 3261.
[120] V. Ruehle, C. Junghans, A. Lukyanov, K. Kremer, D. Andrienko, J. Chem. Theory Comput. 2009, 5, 3211 – 3223.
[121] S. Verlaak, P. Herremans Phys. Rev. B 2007, 75, 115127.
[122] J. Kirkpatrick, V. Marcon, K. Kremer, J. Nelson, D. Andrienko, J. Chem. Phys. 2008, 129, 094506.
[123] H. Bssler, Phys. Status Solidi B 1993, 175, 15 – 56.
[124] J. F. Chang, T. Sakanoue, Y. Olivier, T. Uemera, M. B. Dufourg-Madec, S. G. Yeates, J. Cornil, J. Takeya, A. Troisi,
H. Sirringhaus, Phys. Rev. Lett. 2011, 107, 066601.
[125] M. Pope, C. S. Swenberg, Electronic Processes in Organic
Crystals and Polymers, 2nd Ed., Oxford University Press,
Oxford, 1999.
[126] A. J. Heeger, S. Kivelson, J. R. Schrieffer, W. P. Su, Rev.
Mod. Phys. 1988, 60, 781 – 850.
[127] A. Troisi, G. Orlandi, J. Phys. Chem. A 2006, 110, 4065 –
4070.
[128] M. Schrader, R. Fitzner, M. Hein, C. Elschner, B. Baumeier, K. Leo, M. Riede, P. Buerle, D. Andrienko, J. Am.
Chem. Soc. 2012, 134, 6052 – 6056.
[129] L. J. Wang, Q. K. Li, Z. Shuai, L. P. Chen, Q. Shi, Phys.
Chem. Chem. Phys. 2010, 12, 3309.
[130] F. Oton, R. Pfattner, N. S. Oxtoby, M. Mas-Torrent, K.
Wurst, X. Fontrodona, Y. Olivier, J. Cornil, J. Veciana, C.
Rovira, J. Org. Chem. 2011, 76, 154 – 163.
[131] F. Oton, R. Pfattner, E. Pavlica, Y. Olivier, E. Moreno, J.
Puigdollers, G. Bratina, J. Cornil, X. Fontrodona, M. MasTorrent, J. Veciana, C. Rovira, Chem. Mater. 2011, 23,
851 – 861.
Isr. J. Chem. 2013, 53, 1 – 27
[132] Y. Olivier, L. Muccioli, C. Zannoni, J. Cornil, AIP Conf.
Proc. 2008, 1046, 32 – 35.
[133] V. C. Sundar, J. Zaumseil, V. Podzorov, E. Menard, R. L.
Willett, T. Someya, M. E. Gershenson, J. A. Rogers, Science 2004, 303, 1644 – 1646.
[134] T. Holstein, Ann. Phys. 1959, 8, 325 – 342.
[135] T. Holstein, Ann. Phys. 1959, 8, 343 – 389.
[136] K. Hannewald, V. M. Stojanović, J. M. T. Schellekens, P. A.
Bobbert, G. Kresse, J. Hafner, Phys. Rev. B 2004, 69,
75211.
[137] K. Hannewald, P. A. Bobbert, Phys. Rev. B 2004, 69,
75212.
[138] K. Hannewald, P. A. Bobbert, Appl. Phys. Lett. 2004, 85,
1535.
[139] F. Ortmann, F. Bechstedt, K. Hannewald, Phys. Rev. B
2009, 79 235206.
[140] F. Ortmann, F. Bechstedt, K. Hannewald, Phys. Status
Solidi B 2009, 248, 511 – 525.
[141] A. Troisi, G. Orlandi, Phys. Rev. Lett. 2006, 96, 086601.
[142] M. Hultell, S. Stafstrçm, Chem. Phys. Lett. 2006, 428, 446 –
450.
[143] S. Stafstrçm, Chem. Soc. Rev. 2010, 39, 2484 – 2499.
[144] A. Troisi, Adv. Mater. 2007, 19, 2000 – 2004.
[145] L. Wang, D. Beljonne, J. Phys. Chem. Lett. 2013, 4, 1888 –
1894.
[146] J. Veres, S. D. Ogier, S. W. Leeming, D. C. Cupertino, S. M.
Khaffaf, Adv. Funct. Mater. 2003, 13, 199 – 204.
[147] C. Kim, A. Facchetti, T. J. Marks, Science 2007, 318, 76 –
80. >
[148] N. Benson, C. Melzer, R Schmechel, H. von Seggern, Phys.
Status Solidi A 2008, 205, 475 – 487.
[149] R. P. Ortiz, A. Facchetti, T. J. Marks, Chem. Rev. 2010, 110,
205 – 239.
[150] C. Tanase, E. J. Meijer, P. W. M. Blom, D. M. de Leeuw,
Phys. Rev. Lett. 2003, 91, 216601.
[151] W. F. Pasveer, J. Cottaar, C. Tanase, R. Coehoorn, P. A.
Bobbert, P. W. M. Blom, D. M. de Leeuw, M. A. J. Michels,
Phys. Rev. Lett. 2005, 94, 206601.
[152] D. Kondepudi, I. Prigogine, Modern Thermodynamics:
From Heat Engines to Dissipative Structures, Wiley-VCH,
Weinheim, 1998.
[153] R. Landauer, J. Stat. Phys. 1975, 13, 1 – 16.
[154] R. Landauer, Phys. Rev. A 1975, 12, 636 – 638.
[155] S. Bruers, C. Maes, K. Netočnỳ, J. Stat. Phys. 2007, 129,
725 – 740.
[156] T. Yuge, http://arxiv.org/abs/1309.0848, cond-mat.statmech.
[157] S.-i. Sasa, H. Tasaki, J. Stat. Phys. 2006, 125, 125 – 224.
[158] C. Bustamante, J. Liphardt, F. Ritort, Phys. Today 2005, 58,
43 – 48.
[159] Y. Olivier, V. Lemaur, J. L. Brdas, J. Cornil, J. Phys.
Chem. 2006, 110, 6356 – 6364.
[160] T. Sakanoue, H. Sirringhaus, Nat. Mater. 2010, 9, 736 – 740.
[161] D. G. Cahill, MRS Bull. 2012, 37, 855 – 863.
[162] Y. Xu, C. Liu, Y. Li, T. Minari, P. Darmawan, F. Balestra,
G. Ghibaudo, K. Tsukagoshi, J. Appl. Phys. 2013, 113,
064507.
[163] D. Wang, L. Tang, M. Long, Z. Shuai, J. Phys. Chem. C
2011, 115, 5940 – 5946.
[164] J. Chen, D. Wang, Z. Shuai, J. Chem. Theory Comput.
2012, 8, 3338 – 3347.
[165] H. A. Patel, S. Garde, P. Keblinski, Nano Lett. 2005, 5,
2225 – 2231.
[166] Y. Wang, P. Keblinski, J. Appl. Phys. 2012, 111, 064321.
2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.ijc.wiley-vch.de
&21&
These are not the final page numbers! ÞÞ
Review
[167] V. Botan, E. H. G. Backus, R. Pfister, A. Moretto, M.
Crisma, C. Toniolo, P. H. Nguyen, G. Stock, P. Hamm,
Proc. Natl. Acad. Sci. USA 2007, 104, 12749 – 12754.
[168] S. G. J. Mathijssen, M.-J. Spijkman, A.-M. Andringa, P. A.
van Hal, I. McCulloch, M. Kemerink, R. A. J. Janssen,
D. M. de Leeuw, Adv. Mater. 2010, 22, 5105 – 5109.
[169] O. Bubnova, Z. U. Khan, A. Malti, S. Braun, M. Fahlman,
M. Berggren, X. Crispin, Nat. Mater. 2011, 10, 429 – 433.
[170] D. Wang, W. Shi, J. Chen, J. Xi, Z. Shuai, Phys. Chem.
Chem. Phys. 2012, 14, 16505 – 16520.
[171] G.-H. Kim, L. Shao, K. Zhang, K. P. Pipe Nat. Mater. 2013,
12, 719 – 723.
[172] O. Bubnova, M. Berggren, X. Crispin, J. Am. Chem. Soc.
2012, 134, 16456 – 16459.
[173] P. Gaspard, Phys. A 2006, 369, 201 – 246.
[174] R. Ruiz, D. Choudhary, B. Nickel, T. Toccoli, K.-C. Chang,
A. C. Mayer, P. Clancy, J. M. Blakely, R. L. Headrick, S.
Iannotta, G. G. Malliaras, Chem. Mater. 2004, 16, 4497 –
4508.
[175] C. M. Duffy, J. W. Andreasen, D. W. Breiby, M. M. Nielsen,
M. Ando, T. Minakata, H. Sirringhaus, Chem. Mater. 2008,
20, 7252 – 7259.
[176] S. Yogev, R. Matsubara, M. Nakamura, Y. Rosenwaks,
Org. Electron. 2010, 11, 1729 – 1735.
[177] A. Shehu, S. D. Quiroga, P. DAngelo, C. Albonetti, F. Borgatti, M. Murgia, A. Scorzoni, P. Stoliar, F. Biscarini, Phys.
Rev. Lett. 2010, 104, 246602.
[178] S. Kowarik, K. Broch, A. Hinderhofer, A. Schwartzberg, J.
Oriol Oss
, D. Kilcoyne, F. Schreiber, S. R. Leone, J. Phys.
Chem. C 2010, 114, 13061 – 13067.
[179] B. Bruer, A. Virkar, S. C. B. Mannsfeld, D. P. Bernstein,
R. Kukreja, K. W. Chou, T. Tyliszczak, Z. Bao, Y. Acremann, Chem. Mater. 2010, 22, 3693 – 3697.
[180] H. Jiang, K. J. Tan, K. K. Zhang, X. Chen, C. Kloc, J.
Mater. Chem. 2011, 21, 4771 – 4773.
[181] H. U. Khan, M. E. Roberts, W. Knoll, Z. Bao, Chem.
Mater. 2011, 23, 1946 – 1953.
[182] X. Sun, Y. Liu, C.-a. Di, Y. Wen, Y. Guo, L. Zhang, Y.
Zhao, G. Yu, Adv. Mater. 2011, 23, 1009 – 1014.
[183] I. Salzmann, G. Heimel, S. Duhm, M. Oehzelt, P. Pingel,
B. M. George, A. Schnegg, K. Lips, R.-P. Blum, A. Vollmer, N. Koch, Phys. Rev. Lett. 2012, 108, 035502.
[184] H. Li, B. C.-K. Tee, G. Giri, J. W. Chung, S. Y. Lee, Z. Bao,
Adv. Mater. 2012, 24, 2588 – 2591.
[185] C. Fan, A. P. Zoombelt, H. Jiang, W. Fu, J. Wu, W. Yuan,
Y. Wang, H. Li, H. Chen, Z. Bao, Adv. Mater. 2013, 25,
5762 – 5766.
[186] K. S. Park, B. Cho, J. Baek, J. K. Hwang, H. Lee, M. M.
Sung, Adv. Funct. Mater. 2013, 23, 4776 – 4784.
[187] H. E. Katz, Chem. Mater. 2004, 16, 4748 – 4756.
[188] M. Feng, J. Zhao, T. Huang, X. Zhu, H. Petek, Acc. Chem.
Res. 2011, 44, 360 – 368.
[189] T. D. Anthopoulos, C. Tanase, S. Setayesh, E. J. Meijer,
J. C. Hummelen, P. W. M. Blom, D. M. de Leeuw, Adv.
Mater. 2004, 16, 2174 – 2179.
[190] R. Dabirian, X. Feng, L. Ortolani, A. Liscio, V. Morandi,
K. Mullen, P. Samori, V. Palermo, Phys. Chem. Chem.
Phys. 2010, 12, 4473 – 4480.
[191] G. DAvino, S. Mothy, L. Muccioli, C. Zannoni, L. Wang, J.
Cornil, D. Beljonne, F. Castet, J. Phys. Chem. C 2013, 117,
12981.
[192] M. Wang, J. Li, G. Zhao, Q. Wu, Y. Huang, W. Hu, X.
Gao, H. Li, D. Zhu, Adv. Mater. 2013, 25, 2229 – 2233.
Isr. J. Chem. 2013, 53, 1 – 27
[193] J. Chen, C. K. Tee, J. Yang, C. Shaw, M. Shtein, J. Anthony,
D. C. Martin, J. Polym. Sci. Part B Polym. Phys. 2006, 44,
3631 – 3641.
[194] R. Hamilton, J. Smith, S. Ogier, M. Heeney, J. E. Anthony,
I. McCulloch, J. Veres, D. D. C. Bradley, T. D. Anthopoulos, Adv. Mater. 2009, 21, 1166 – 1171.
[195] R. J. Kline, S. D. Hudson, X. Zhang, D. J. Gundlach, A. J.
Moad, O. D. Jurchescu, T. N. Jackson, S. Subramanian, J. E.
Anthony, M. F. Toney, L. J. Richter, Chem. Mater. 2011, 23,
1194 – 1203.
[196] S. S. Lee, M. A. Loth, J. E. Anthony, Y.-L. Loo, J. Am.
Chem. Soc. 2012, 134, 5436 – 5439.
[197] S. S. Lee, S. Muralidharan, A. R. Woll, M. A. Loth, Z. Li,
J. E. Anthony, M. Haataja, Y.-L. Loo, Chem. Mater. 2012,
24, 2920 – 2928.
[198] S. S. Lee, S. B. Tang, D.-M. Smilgies, A. R. Woll, M. A.
Loth, J. M. Mativesky, J. E. Anthony, Y.-L. Loo, Adv.
Mater. 2012, 24, 2692 – 2698.
[199] L. Yu, X. Li, J. Smith, S. Tierney, R. Sweeney, B. K. C.
Kjellander, G. H. Gelinck, T. D. Anthopoulos, N. Stingelin,
J. Mater. Chem. 2012, 22, 9458 – 9461.
[200] R. Li, H. U. Khan, M. M. Payne, D.-M. Smilgies, J. E. Anthony, A. Amassian, Adv. Funct. Mater. 2013, 23, 291 – 297.
[201] D. T. James, J. M. Frost, J. Wade, J. Nelson, J.-S. Kim, ACS
Nano 2013, 7, 7983 – 7991.
[202] Y. Mei, M. A. Loth, M. Payne, W. Zhang, J. Smith, C. S.
Day, S. R. Parkin, M. Heiney, I. McCulloch, T. D. Anthopoulos, J. E. Anthony, O. D. Jureschu, Adv. Mater. 2013, 25,
4352 – 4357.
[203] V. Podzorov, E. Menard, A. Borissov, V. Kiryukhin, J. A.
Rogers, M. E. Gershenson, Phys. Rev. Lett. 2004, 93,
086602.
[204] Z. Q. Li, V. Podzorov, N. Sai, M. C. Martin, M. E. Gershenson, M. Di Ventra, D. N. Basov, Phys. Rev. Lett. 2007, 99,
016403.
[205] D. A. da Silva Filho, E.-G. Kim, J.-L. Brdas, Adv. Mater.
2005, 17, 1072 – 1076.
[206] D. Kfer, G. Witte, Phys. Chem. Chem. Phys. 2005, 7,
2850 – 2853.
[207] I. N. Hulea, S. Fratini, H. Xie, C. L. Mulder, N. N. Iossad,
G. Rastelli, S. Ciuchi, A. F. Morpugo, Nat. Mater. 2006, 5,
982 – 986.
[208] R. Zeis, C. Besnard, T. Siegrist, C. Schlockermann, X. Chi,
C. Kloc, Chem. Mater. 2006, 18, 244 – 248.
[209] B. D. Chapman, A. Checco, R. Pindak, T. Siegrist, C. Kloc,
J. Cryst. Growth 2006, 290, 479 – 484.
[210] T. Kaji, T. Takenobu, A. F. Morpurgo, Y. Iwasa, Adv.
Mater. 2009, 21, 3689 – 3693.
[211] Z. Li, J. Du, Q. Tang, F. Wang, J. B. Xu, J. C. Yu, Q. Miao,
Adv. Mater. 2010, 22, 3242 – 3246.
[212] H. Najafov, D. Mastrogiovanni, E. Garfunkel, L. C. Feldman, V. Podzorov, Adv. Mater. 2011, 23, 981 – 985.
[213] Y. Chen, B. Lee, D. Fu, V. Podzorov, Adv. Mater. 2011, 23,
5370 – 5375.
[214] P. Irkhin, I. Biaggio, Phys. Rev. Lett. 2011, 107, 017402.
[215] Y. Okada, M. Uno, Y. Nakazawa, K. Sasai, K. Matsusaka,
M. Yoshimura, Y. Kitaoka, Y. Mori, J. Takeya, Phys. Rev.
B 2011, 83, 113305.
[216] I. Gutirrez Lezama, M. Nakano, N. A. Minder, Z. Chen,
F. V. Di Girolamo, A. Facchetti, A. F. Morpurgo, Nat.
Mater. 2012, 11, 788 – 794.
[217] M. A. Reyes-Martinez, A. Ramasubramaniam, A. J. Briseno, A. J. Crosby, Adv. Mater. 2012, 24, 5548 – 5552.
2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.ijc.wiley-vch.de
&22&
These are not the final page numbers! ÞÞ
Review
[218] B. Lee, Y. Chen, D. Fu, H. T. Yi, K. Czelen, H. Najafov, V.
Podzorov, Nat. Mater. 2013, 12, 1125 – 1129.
[219] W. Xie, P. L. Prabhumirashi, Y. Nakayama, K. A. McGarry,
M. L. Geier, Y. Uragami, K. Mase, C. J. Douglas, H Ishii,
M. C. Hersam, C. D. Frisbie, ACS Nano 2013, 7, 10245 –
10256.
[220] A. S. Paraskar, A. R. Reddy, A. Patra, Y. H. Wijsboom, O.
Gidron, L. J. W. Shimon, G. Leitus, M. Bendikov, Chem.
Eur. J. 2008, 14, 10639 – 10647.
[221] K. A. McGarry, W. Xie, C. Sutton, C. Risko, Y. Wu, V. G.
Young, Jr., J.-B. Brdas, C. D. Frisbie, C. J. Douglas, Chem.
Mater. 2013, 25, 2254 – 2263.
[222] T. K. Mullenbach, K. A. McGarry, W. A. Luhman, C. J.
Douglas, R. J. Holmes, Adv. Mater. 2013, 25, 3689 – 3693.
[223] F. Anger, R. Scholz, E. Adamski, K. Broch, A. Gerlach, Y.
Sakamoto, T. Suzuki, F. Schreiber, Appl. Phys. Lett. 2013,
102, 013308.
[224] W. Xie, K. A. McGarry, F. Liu, Y. Wu, P. P. Ruden, C. J.
Douglas, C. D. Frisbie, J. Phys. Chem. C, 2013, 117, 11522 –
11529.
[225] H. Ebata, T. Izawa, E. Miyazaki, K. Takimiya, M. Ikeda,
H. Kuwabara, T. Yui, J. Am. Chem. Soc. 2007, 129, 15732 –
15733.
[226] T. Izawa, E. Miyazaki, K. Takimiya, Adv. Mater. 2008, 20,
3388 – 3392.
[227] M. Kano, T. Minari, K. Tsukagoshi, Appl. Phys. Lett. 2009,
94, 143304.
[228] M.-J. Kang, T. Yamamoto, S. Shinamura, E. Miyazaki, K.
Takimiya, Chem. Sci. 2010, 1, 179 – 183.
[229] H. Tanaka, M. Kozuka, S.-i. Watanabe, H. Ito, Y. Shimoi,
K. Takimiya, S.-i. Kuroda, Phys. Rev. B 2011, 84,
081306(R).
[230] J. E. Northrup, Appl. Phys. Lett. 2011, 99, 062111.
[231] C. Liu, T. Minari, X. Lu, A. Kumatani, K. Takimiya, K.
Tsukagoshi, Adv. Mater. 2011, 23, 523 – 526.
[232] H. Lino, J.-i. Hanna, Adv. Mater. 2011, 23, 1748 – 1751.
[233] M. Uno, K. Nakayama, J. Soeda, Y. Hirose, K. Miwa, T.
Uemura, A. Nakao, K. Takimiya, J. Takeya, Adv. Mater.
2011, 23, 3047 – 3051.
[234] J. Soeda, Y. Hirose, M. Yamagishi, A. Nakao, T. Uemura,
K. Nakayama, M. Uno, Y. Nakazawa, K. Takimiya, J.
Takeya, Adv. Mater. 2011, 23, 3309 – 3314.
[235] Y. Li, C. Liu, A. Kumatani, P. Darmawan, T. Minari, K.
Tsukagoshi, Org. Electron. 2012, 13, 264 – 272.
[236] R. Nakahara, M. Uno, T. Uemura, K. Takimiya, J. Takeya,
Adv. Mater. 2012, 24, 5212 – 5216.
[237] J. Jang, S. Nam, K. Im, J. Hur, S. N. Cha, J. Kim, H. B. Son,
H. Suh, M. A. Loth, J. E. Anthony, J.-J. Park, C. E. Park,
J. M. Kim, K. Kim, Adv. Funct. Mater. 2012, 22, 1005 –
1014.
[238] T. Yokota, K. Kuribara, T. Tokuhara, U. Zschieschang, H.
Klauk, K. Takimiya, Y. Sadamitsu, M. Hamada, T. Sekitani, T. Someya, Adv. Mater. 2013, 25, 3639 – 3644.
[239] C. Liu, Y. Xu, Y. Li, W. Scheideler, T. Minari, J. Phys.
Chem. C 2013, 117, 12337 – 12345.
[240] L. Huang, M. Stolte, H. Brckstmmer, F. Wrthner, Adv.
Mater. 2012, 24, 5750 – 5754.
[241] E. D. Głowacki, M. Irimia-Vladu, M. Kaltenbrunner, J.
Gsiorowski, M. S. White, U. Monkowius, G. Romanazzi,
G. P. Suranna, P. Mastrorilli, T. Sekitani, S. Bauer, T.
Someya, L. Torsi, N. S. Sariciftci, Adv. Mater. 2013, 25,
1563 – 1569.
[242] J. Tant, Y. H. Geerts, M. Lehmann, V. De Cupere, G.
Zucchi, B. W. Laursen, T Bjørnholm, V. Lemaur, V.
Isr. J. Chem. 2013, 53, 1 – 27
[243]
[244]
[245]
[246]
[247]
[248]
[249]
[250]
[251]
[252]
[253]
[254]
[255]
[256]
[257]
[258]
[259]
[260]
[261]
[262]
[263]
[264]
[265]
[266]
[267]
[268]
[269]
[270]
Marcq, A. Burquel, E. Hennebicq, F. Gardebien, P. Viville,
D. Beljonne, R. Lazzaroni, J. Cornil, J. Phys. Chem. B
2005, 109, 20315 – 20323.
R. S. Snchez-Carrera, S. Atahan, J. Schrier, A. AspuruGuzik, J. Phys. Chem. C 2010, 114, 2334 – 2340.
Y. Nakayama, Y. Uragami, S.i. Machida, K. R. Koswattage, D. Yoshimura, H. Setoyama, T. Okajima, K. Mase, H.
Ishii, Appl. Phys. Express 2012, 5, 111601.
D. B. A. Rep, A. F. Morpugo, W. G. Sloof, T. M. Klapwiijk,
J. Appl. Phys. 2003, 93, 2082 – 2090.
F. C. Krebs, R. B. Nyberg, M. Jørgensen, Chem. Mater.
2004, 16, 1313 – 1318.
M. Funahashi, J.-i. Hanna, Chem. Phys. Lett. 2004, 397,
319 – 323.
A. Voloshenko, K. J. Tan, C. Kloc, O. Lev. M. Shelkov, S.
Sladkevich, P. V. Prikhodchenko, J. Gun, Org. Electron.
2013, 14, 378 – 388.
J. E. Anthony, private communication.
O. D. Jurchescu, S. Subramanian, R. J. Kline, S. D. Hudson,
J. E. Anthony, T. N. Jackson, D. J. Gundlach, Chem. Mater.
2008, 20, 6733 – 6737.
V. De Cupere, J. Tant, P. Viville, R. Lazzaroni, W. Osikowicz, W. R. Salaneck, Y. H. Geerts, Langmuir 2006, 22,
7798 – 7806.
M. Schwoerer, H.-C. Wolf, Organic Molecular Solids,
Wiley-VCH, Weinheim, 2007.
W. R. Wilcox, R. Friedenberg, N. Back, Chem. Rev. 1964,
64, 187 – 220.
N. Karl in Crystals: Growth, Properties, and Applications,
Vol. 4 (Ed.: H. C. Freyhardt), Springer, Heidelberg, 1980.
I. H. Hong, K. J. Tan, M. Toh, H. Jiang, K. Zhang, C. Kloc,
J. Cryst. Growth 2013, 363, 61 – 68.
O. Roussel, Ph.D. Thesis, Universit Libre de Bruxelles
(Belgium), 2006.
Y. Roichman N. Tessler, Appl. Phys. Lett. 2002, 80, 1948 –
1950.
G. Horowitz, J. Mater. Res. 2004, 19, 1946 – 1962.
I. Salzmann, S. Duhm, R. Opitz, J. P. Rabe, N. Koch, Appl.
Phys. Lett. 2007, 91, 051919.
P. A. Bobbert, A. Sharma, S. G. J. Mathijssen, M. Kemerink, D. M. de Leeuw, Adv. Mater. 2012, 24, 1146 – 1158.
B. J. McArdle, J. N. Sherwood, A. C. Damask, J. Cryst.
Growth 1974, 22, 193 – 200. R. S. Narang, B. S. Shah, N.
Sherwood, J. Cryst. Growth 1974, 22, 201 – 209.
D. T. J. Hurle, P. Rudolph, J. Cryst. Growth 2004, 264, 550 –
564.
H. Ade, H. Stoll, Nat. Mater. 2009, 8, 281 – 290.
D. M. DeLongchamp, R. J. Kline, D. A. Fischer, L. J.
Richter, M. F. Toney, Adv. Mater. 2011, 23, 319 – 337.
B. Watts, H. Ade, Mater. Today 2012, 15, 148 – 157.
A. Salleo, R. J. Kline, D. M. DeLongchamp, M. Chabinyc,
Adv. Mater. 2010, 22, 3812 – 3838.
B. A. Collins, J. E. Cochran, H. Yan, E. Gann, C. Hub, R.
Fink, C. Wang, T. Schuettfort, C. R. McNeill, M. L. Chabinyc, H. Ade, Nat. Mater. 2012, 11, 536 – 543.
J. Rivnay, R. Noriega, R. J. Kline, A. Salleo, M. F. Toney,
Phys. Rev. B 2011, 84, 045203.
M. Tello, M. Chiesa, C. M. Duffy, H. Sirringhaus, Adv.
Funct. Mater. 2008, 18, 3907 – 3913.
J. Rivnay, L. H. Jimison, J. E. Northrup, M. F. Toney, R.
Noriega, S. Lu, T. J. Marks, A. Facchetti, A. Salleo, Nat.
Mater. 2009, 8, 952 – 958.
2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.ijc.wiley-vch.de
&23&
These are not the final page numbers! ÞÞ
Review
[271] R. Li, J. W. Ward, D. M. Smilgies, M. M. Payne, J. E. Anthony, O. D. Jurchescu, A. Amassian, Adv. Mater. 2012, 24,
5553 – 5558.
[272] J. Smith, R. Hamilton, I. McCulloch, N. Stingelin-Stutzmann, M. Heeney, D. D. C. Bradley, T. D. Anthopoulos, J.
Mater. Chem. 2010, 20, 2562 – 2574.
[273] M. L. Tang, A. D. Reichardt, T. Siegrist, S. C. B. Mannsfeld, Z. Bao, Chem. Mater., 008, 20, 4669 – 4676.
[274] D. Lehnherr, A. R. Waterloo, K. P. Goetz, M. M. Payne, F.
Hampel, J. E. Anthony, O. D. Jurchescu, R. R. Tykwinski,
Org. Lett. 2012, 14, 3660 – 3663.
[275] J. Bernstein, Polymorphism in Molecular Crystals, Clarendon Press, Oxford, 2002. >
[276] J. Bernstein, Cryst. Growth Des. 2011, 11, 632 – 650.
[277] Polymorphism in the Pharmaceutical Industry (Ed.: R. Hilfiker), Wiley-VCH, Weinheim, 2006.
[278] M. A. Spackman, D. Jayatilaka, CrystEngComm 2009, 11,
19 – 32.
[279] S. T. Salammal, J.-Y. Balandier, J.-B. Arlin, Y. Olivier, V.
Lemaur, L. Wang, D. Beljonne, J. Cornil, A. R. Kennedy,
Y. H. Geerts, B. Chattopadhyay, J. Phys. Chem. C 2014,
118, 657 – 669.
[280] A. Brillante, I. Bilotti, R. G. Della Valle, E. Venuti, A.
Girlando, CrystEngComm 2008, 10, 937 – 946.
[281] S. E. Fritz, S. M. Martin, C. D. Frisbie, M. D. Ward, M. F.
Toney, J. Am. Chem. Soc. 2004, 126, 4084.
[282] H.-L. Cheng, Y.-S. Mai, W.-Y. Chou, L.-R. Chang, X.-W.
Liang, Adv. Funct. Mater. 2007, 17, 3639 – 3649.
[283] H. Yoshida, K. Inaba, N. Sato, Appl. Phys. Lett. 2007, 90,
181930.
[284] D. Nabok, P. Puschnig, C. Ambrosch-Draxl, O. Werzer, R.
Resel, D.-M. Smilgies, Phys. Rev. B. 2007, 76, 235322.
[285] I. P. M. Bouchoms, W. A. Schoonveld, J. Vrijmoeth, T. M.
Klapwijk, Synth. Met. 1999, 104, 175.
[286] S. C. B. Mannsfeld, A. Virkar, C. Reese, M. F. Toney, Z.
Bao, Adv. Mater. 2009, 21, 2294.
[287] K. Puntambekar, J. Dong, G. Haugstad, C. D. Frisbie, Adv.
Funct. Mater. 2006, 16, 879 – 884.
[288] a) I. Salzmann, D. Nabok, M. Oehzelt, S. Duhm, A. Moser,
G. Heimel, P. Puschnig, C. Ambrosch-Draxl, J. P. Rabe, N.
Koch, Cryst. Growth. Des. 2011, 11, 600 – 606; b) G. Gbabode, N. Dumont, F. Quist, G. Schweicher, A. Moser, P.
Viville, R. Lazzaroni, Y. H. Geerts, Adv. Mater. 2012, 24,
658 – 662.
[289] a) M. Yoneya, M. Kawasaki, M. Ando, J. Phys. Chem. C
2012, 116, 791 – 795; b) W.-Y. Chou, M.-H. Chang, H.-L.
Cheng, Y.-C. Lee, C.-C. Chang, H.-S. Sheu, J. Phys. Chem.
2012, 116, 8619 – 8626; c) H.-L. Cheng, J.-W. Lin, Cryst.
Growth. Des. 2010, 10, 4501 – 4508.
[290] S. C. B. Mannsfeld, M. L. Tang, Z. Bao, Adv. Mater. 2011,
23, 127 – 131.
[291] B. Wedl, R. Resel, G. Leising, B. Kunert, I. Salzmann, M.
Oehzelt, N. Koch, A. Vollmer, S. Duhm, O. Werzer, G.
Gbabode, M. Sferrazza, Y. Geerts, RSC Adv. 2012, 2,
4404 – 4414.
[292] O. Werzer, N. Boucher, J. P. de Silva, G. Gbabode, Y. H.
Geerts, O. Konovalov, A. Moser, J. Novak, R. Resel, M.
Sferrazza, Langmuir 2012, 28, 8530 – 8536.
[293] M. Dohr, O. Werzer, Q. Shen, I. Salzmann, C. Teichert, C.
Ruzie, G. Schweicher, Y. H. Geerts, M. Sferrazza, R.
Resel, ChemPhysChem 2013, 14, 2554 – 2559.
[294] H.-L. Cheng, W.-Y. Chou, C.-W. Kuo, Y.-W. Wang, Y.-S.
Mai, F.-C. Tang, S.-W. Chu, Adv. Funct. Mater. 2008, 18,
285 – 293.
Isr. J. Chem. 2013, 53, 1 – 27
[295] A. Amassian, V. A. Pozdin, T. V. Desai, S. Hong, A. R.
Woll, J. D. Ferguson, J. D. Brock, G. G. Malliaras, J. R.
Engstrom, J. Mater. Chem. 2009, 19, 5580 – 5592.
[296] Q. Jin, D. Li, Q. Qi, Y. Zhang, J. He, C. Jiang, Cryst.
Growth Des. 2012, 12, 5432 – 5438.
[297] G. Schweicher, N. Paquay, C. Amato, R. Resel, M. Koini,
S. Talvy, V. Lemaur, J. Cornil, Y. Geerts, G. Gbabode,
Cryst. Growth Des. 2011, 11, 3663 – 3672.
[298] W. Pisula, A. Menon, M. Stepputat, I. Lieberwirth, U.
Kolb, A. Tracz, H. Sirringhaus, T. Pakula, K. Mllen, Adv.
Mater. 2005, 17, 684 – 689.
[299] W.-Y. Lee, J. H. Oh, S.-L. Suraru, W.-C. Chen, F. Wrthner,
Z. Bao, Adv. Funct. Mater. 2011, 21, 4173 – 4181.
[300] P. S. Jo, A. Vailionis, Y. M. Park, A. Salleo, Adv. Mater.
2012, 24, 3269 – 3274.
[301] A. Kumatami, C. Liu, Y. Li, P. Darmawan, K. Takimiya, T.
Minari, K. Tsukagoshi, Sci. Rep. 2012, 2, 393.
[302] P. J. Collings, M. Hird, Introduction to Liquid Crystals:
Chemistry and Physics, CRC Press, Boca Raton, 1997.
[303] P. A. Heiney, J. E. Fischer, A. R. McGhie, W. J. Romanow,
A. M. Denenstein, J. P. McCauley, A. B. Smith, Phys. Rev.
Lett. 1991, 66, 2911 – 2914.
[304] H. Tamura, M. Tsukada, Phys. Rev. B 2012, 85, 054301.
[305] Liquid Crystalline Semiconductors (Eds.: R. J. Bushby,
S. M. Kelly, M. ONeill), Springer, Dordrecht, 2013.
[306] M. ONeill, S. M. Kelly, Adv. Mater. 2003, 15, 1135 – 1146.
[307] Y. Shimizu, K. Oikawa, K.-i Nakayama, D. Guillon, J.
Mater. Chem. 2007, 17, 4223 – 4229.
[308] M. ONeill, S. M. Kelly, Adv. Mater. 2011, 23, 566 – 584.
[309] E. Pouzet, V. De Cupere, C. Heintz, J. W. Andreasen,
D. W. Breiby, M. M. Nielsen, P. Viville, R. Lazzaroni, G.
Gbabode, Y. H. Geerts, J. Phys. Chem. C 2009, 113,
14398 – 14406.
[310] G. Schweicher, G. Gbabode, F. Quist, O. Debever, N.
Dumont, S. Sergeyev, Y. H. Geerts, Chem. Mater. 2009, 21,
5867 – 5874.
[311] A Tracz, T. Makowski, S. Masirek, W. Pisula, Y. H. Geerts,
Nanotechnology 2007, 18, 485303.
[312] P.-O. Mouthuy, S. Melinte, Y. H. Geerts, A. M. Jonas, Nano
Lett. 2007, 7, 2627 – 2632.
[313] P.-O. Mouthuy, S. Melinte, Y. H. Geerts, B. Nysten, A. M.
Jonas, Small 2008, 4, 728 – 732.
[314] M. Cavallini, A. Calo, P. Stoliar, J. C. Kengne, S. Martins,
F. C. Matacotta, F. Quist, G. Gbabode, N. Dumont, Y. H.
Geerts, F. Biscarini, Adv. Mater. 2009, 21, 4688 – 4691.
[315] K. Oikama, H. Monobe, K.-i. Nakayama, T. Kimoto, K.
Tsuchiya, B. Heinrich, D. Guillon, Y. Shimizu, M. Yokoyama, Adv. Mater. 2007, 19, 1864 – 1868.
[316] J.-i. Hanna in Liquid Crystalline Semiconductors (Eds.:
R. J. Bushby, S. M. Kelly, M. ONeill), Springer, Dordrecht,
2013, Chapter 2.
[317] H. Lino, J.-i. Hanna, Adv. Mater. 2011, 23, 1748 – 1751.
[318] a) H. Lino, T. Usui, T. Kobori, J. Hanna, Dig. Tech. Pap.
Soc. Inf. Disp. Int. Symp. 2012, 497 – 500; b) Z. An, J. Yu,
S. C. Jones, S. Barlow, S. Yoo, B. Domercq, P. Prins, Laurens D. A. Siebbeles, B. Kippelen, S. R. Marder, Adv.
Mater. 2005, 17, 2580 – 2583; c) Y. Miyake, Y. Shiraiwa, K.
Okada, H. Monobe, T. Hori, N. Yamasaki, H. Yoshida,
M. J. Cook, A. Fujii, M. Ozaki, Y. Shimizu, Appl. Phys.
Express 2011, 4, 021604.
[319] S. Sergeyev, W. Pisula, Y. H. Geerts, Chem. Soc. Rev. 2007,
36, 1902 – 1929.
[320] Y. C. Cheng, R. J. Silbey, D. A. da Silva Filho, J. P. Calbert,
J. L. Brdas, J. Chem. Phys. 2003, 118, 3764 – 3774.
2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.ijc.wiley-vch.de
&24&
These are not the final page numbers! ÞÞ
Review
[321] A. Corval, R. Casalegno, S. Astilean, H. P. Trommsdorff, J.
Phys. Chem. 1992, 96, 5393 – 5395.
[322] M. S. Deleuze, L. Claes, E. S. Kryachko, J.-P. FranÅois, J.
Chem. Phys. 2003, 119, 3106 – 3119.
[323] A. Devos, M. Lannoo, Phys. Rev. B 1998, 58, 8236.
[324] N. G. Martinelli, Y. Olivier, M. C. Ruiz Delgado, K. R.
Pigg, D. A. da Silva Filho, R. S. Sanchez-Carrera, E.
Venuti, R. G. Della Valle, J. L. Brdas, D. Beljonne, J.
Cornil, ChemPhysChem 2009, 13, 2265 – 2273.
[325] Y. Lee, S. Roth, Y. W. Park, Appl. Phys. Lett. 2006, 88,
252106.
[326] C. Reese, Z. Bao, Adv. Mat. 2007, 19, 4535 – 4538.
[327] O. Ostroverkhova, D. G. Cooke, F. A. Hegmann, R. R.
Tykwinski, S. R. Parkin, J. E. Anthony, Appl. Phys. Lett.
2006, 89, 192113.
[328] T. Vehoff, B. Baumeier, A. Troisi, D. Andrienko, J. Am.
Chem. Soc. 2010, 132, 11702 – 11708.
[329] T. Vehoff, Y. S. Sook, K. Johnston, A. Troisi, D. Y. Yoon,
D. Andrienko, J. Phys. Chem. 2010, 114, 10592 – 10597.
[330] S. G. J. Mathijssen, E. C. P. Smits, P. A. van Hal, H. J. Wondergem, S. A. Ponomarenko, A. Moser, R. Resel, P. A.
Bobbert, M. Kemerink, R. A. J. Janssen, D. M. de Leeuw,
Nat. Nanotechnol. 2009, 4, 674 – 680.
[331] F. Dinelli, M. Murgia, P. Levy, M. Cavallini, F. Biscarini,
Phys. Rev. Lett. 2004, 92, 116802.
[332] P. Hartman, P. Bennema, J. Cryst. Growth 1980, 49, 145 –
156.
[333] M. Treier, J.-B. Arlin, C. Ruzie, Y. H. Geerts, V. Lemaur, J.
Cornil, P. Samori, J. Mater. Chem. 2012, 22, 9509 – 9512.
[334] G. Schweicher, Ph.D. Thesis, Universit Libre de Bruxelles
(Belgium), 2012.
[335] Materials Studio v5.0.0.0, Accelrys Software Inc., San
Diego, 2009.
[336] H. J. Sun, Phys. Chem. B 1998, 102, 7338 – 7364.
[337] A. Facchetti, M.-H Yoon, T. J. Marks, Adv. Mater. 2005, 17,
1705 – 1725.
[338] Y. D. Park, J. A. Lim, H. S. Lee, K. Cho, Mater. Today
2007, 10, 46 – 54.
[339] X. Sun, C.-a. Di, Y. Liu, J. Mater. Chem. 2010, 20, 2599 –
2611.
[340] A. F. Stassen, R. W. I. de Boer, N. N. Iosad, A. F. Morpugo,
Appl. Phys. Lett. 2004, 85, 3899 – 3901.
[341] Y. Xia, J. H. Cho, J. Lee, P. P. Ruden, C. D. Frisbie, Adv.
Mater. 2009, 21, 2174 – 2179.
[342] L. L. Chua, J. Zaumseil, J. F. Chang, E. C. W. Ou, P. K. H.
Ho, H. Sirringhaus, R. H. Friend, Nature 2005, 434, 194 –
199.
[343] S. Steudel, S. De Vusser, S. De Jonge, D. Janssen, S. Verlaak, J. Genoe, P. Heremans, Appl. Phys. Lett. 2004, 85,
4400.
[344] C. Kim, A. Facchetti, T. J. Marks, Adv. Mater. 2007, 19,
2561 – 2566.
[345] K.-J. Baeg, D. Khim, S.-W. Jung, M. Kang, I.-K. You, D.-Y.
Kim, A. Facchetti, Y-Y. Noh, Adv. Mater. 2012, 24, 5433 –
5439.
[346] M. F. Calhoun, J. Sanchez, D. Olaya, M. E. Gershenson, V.
Podzorov, Nat. Mater. 2008, 7, 84 – 89.
[347] B. Lee, T. Choi, S.-W. Cheong, V. Podzorov, Adv. Funct.
Mater. 2009, 19, 3726 – 3730.
[348] H. Mndez, G. Heimel, A. Opitz, K. Sauer, P. Barkowski,
M. Oehzelt, J. Soeda, T. Okamoto, J. Takeya, J.-B. Arlin,
J.-Y. Balandier, Y. Geerts, N. Koch, I. Salzmann, Angew.
Chem. Int. Ed. 2013, 52, 7751 – 7755.
Isr. J. Chem. 2013, 53, 1 – 27
[349] O. Larsson, A. Laiho, W. Schmickler, M. Berggren, X.
Crispin, Adv. Mater. 2011, 23, 4764 – 4769.
[350] H. T. Yi, Y. Chen, K. Czelen, V. Podzorov, Adv. Mater.
2011, 23, 5807 – 5811.
[351] Y. Zhang, H. Dong, Q. Tang, S. Ferdous, F. Liu, S. C. B.
Mannsfeld, W. Hu, A. L. Briseno, J. Am. Chem. Soc. 2010,
132, 11580 – 11584.
[352] D. Beljonne, J. Cornil, L. Muccioli, C. Zannoni, J.-L.
Brdas, F. Castet, Chem. Mater. 2011, 23, 591 – 609.
[353] H. Geng, Q. Peng, L. Wang, H. Li, Y. Liao, Z. Ma, Z.
Shuai, Adv. Mater. 2012, 24, 3568 – 3572.
[354] Y. Li, V. Coropceanu, J.-L. Brdas, J. Phys. Chem. Lett.
2012, 3, 3325 – 3329.
[355] Z. Rang, M. I. Nathan, P. P. Ruden, V. Podzorov, M. E.
Gershenson, C. R. Newman, C. D. Frisbie, Appl. Phys.
Lett. 2005, 86, 123501.
[356] C.-Y. Liu, A. J. Bard, Nature, 2002, 418, 162.
[357] H. Klauk, G. Schmid, W. Radlik, W. Weber, L. Zhou, C. D.
Sheraw, J. A. Nichols, T. N. Jackson, Solid-State Electron.
2003, 47, 297 – 301.
[358] A. Molinary, I. Gutirrez, L. N. Hulea, S. Russo, A. Morpugo, Appl. Phys. Lett. 2007, 90, 212103.
[359] G. Heimel, L. Romaner, E. Zojer, J. L. Brdas, Acc. Chem.
Res. 2008, 41, 721 – 729.
[360] C. M. Cardona, W. Li, A. E. Kaifer, D. Stockdale, G. C.
Bazan, Adv. Mater. 2011, 23, 2367 – 2371.
[361] A. Mityashin, Y. Olivier, T. Van Regemorter, C. Rolin, S.
Verlaak, N. Martinelli, D. Beljonne, J. Cornil, J. Genoe, P.
Heremans, Adv. Mater. 2012, 24, 1535 – 1539.
[362] S. M. Ryno, S. R. Lee, J. S. Sears, C. Risko, J.-L. Brdas, J.
Phys. Chem. C 2013, 117, 13853 – 13860.
[363] O. Labanova Griffith, J. E. Anthony, A. G. Jones, D. L.
Lichtenberger, J. Am. Chem. Soc. 2010, 132, 580 – 586.
[364] O. Labanova Griffith, A. G. Jones, J. E. Anthony, D. L.
Lichtenberger, J. Phys. Chem. C 2010, 114, 13838 – 13845.
[365] S. Duhm, G. Heimel, I. Salzmann, H. Glowatzki, R. L.
Johnson, A. Vollmer, J. P. Rabe, N. Koch, Nat. Mater. 2008,
7, 326 – 332.
[366] G. Heimel, S. Duhm, I. Salzmann, A. Gerlach, A. Strozecka, J. Niederhausen, C. Brker, T. Hosokai, I. Fernandez-Torrente, G. Schulze, S. Winkler, A. Wilke, R. Schlesinger, J. Frisch, B. Brçker, A. Vollmer, B. Detlefs, J.
Pflaum, S. Kera, K. J. Franke, N. Ueno, J. I. Pascual, F.
Schreiber, N. Koch, Nat. Chem. 2013, 5, 187 – 194.
[367] L. Vitali, G. Levita, A. Comisso, A. De Vita, K. Kern, Nat.
Mater. 2010, 9, 320 – 323.
[368] G. Heimel, L. Romaner, E. Zojer, J. L. Brdas, Nano Lett.
2007, 7, 932 – 940.
[369] X. Y. Cheng, Y. Y. Noh, J. P. Wang, M. Tello, J. Frisch, R. P.
Blum, A. Vollmer, J. P. Rabe, N. Koch, H. Sirringhaus,
Adv. Funct. Mater. 2009, 19, 2407 – 2415.
[370] P. Stollar, R. Kshirsagar, M. Massi, P. Annibale, C. Albonetti, D. M. de Leeuw, F. Biscarini, J. Am. Chem. Soc.
2007, 129, 6477 – 6484.
[371] A. Liscio, E. Orgiu, J. M. Mativetsky, V. Palermo, P.
Samor, Adv. Mater. 2010, 22, 5018 – 5023.
[372] N. Crivillers, E. Orgiu, F. Reinders, M. Mayor, P. Samori,
Adv. Mater. 2011, 23, 1447 – 1452.
[373] M. Marinkovic, D. Belaineh, V. Wagner, D. Knipp, Adv.
Mater. 2012, 24, 4005 – 4009.
[374] G. B. Blanchet, C. R. Fincher, M. Lefenfeld, J. A. Rogers,
Appl. Phys. Lett. 2004, 84, 296 – 298.
2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.ijc.wiley-vch.de
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Review
[375] C. R. Newman, C. D. Frisbie, D. A. da Silva Filho, J. L.
Brdas, P. C. Ewbank, K. R. Mann, Chem. Mater. 2004, 16,
4436 – 4451.
[376] C. Deibel, D. Janssen, P. Heremans, V. De Cupere, Y.
Geerts, M. L. Benkhedir, G. J. Adriaenssens, Org. Electron.
2006, 7, 495 – 499.
[377] V. Podzorov, E. Menard, J. A. Rogers, M. E. Gershenson,
Phys. Rev. Lett. 2005, 95, 226601.
[378] J. Takeya, K. Tsukagoshi, Y. Aoyagi, T. Takenobu, Y.
Isawa, Jpn. J. Appl. Phys. 2005, 44, L1393 – L1396.
[379] Y. Okada, K. Sakai, T. Uemura, Y. Nakazawa, J. Takeya,
Phys. Rev. B 2011, 84, 245308.
Isr. J. Chem. 2013, 53, 1 – 27
[380] E. Menard, V. Podzorov, S.-H. Hur, A. Gaur, M. E. Gershenson, J. A. Rogers, Adv. Mater. 2004, 16, 2097 – 2101.
[381] A. M. van de Craats, P. G. Schouten, J. M. Warman, J. Jpn.
Liq. Cryst. Soc. 1998, 2, 12 – 27.
[382] Y. Honsho, T. Miyakai, T. Sakurai, A. Saeki, S. Seki, Sci.
Rep. 2013, 3, 3182.
Received: February 17, 2014
Accepted: April 12, 2014
Published online: && &&, 0000
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REVIEWS
G. Schweicher, Y. Olivier, V. Lemaur,
Y. H. Geerts*
&& – &&
What Currently Limits Charge
Carrier Mobility in Crystals of
Molecular Semiconductors?
Isr. J. Chem. 2013, 53, 1 – 27
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&27&
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