(This is a sample cover image for this issue. The actual cover is not yet available at this time.)
This article appeared in a journal published by Elsevier. The attached
copy is furnished to the author for internal non-commercial research
and education use, including for instruction at the authors institution
and sharing with colleagues.
Other uses, including reproduction and distribution, or selling or
licensing copies, or posting to personal, institutional or third party
websites are prohibited.
In most cases authors are permitted to post their version of the
article (e.g. in Word or Tex form) to their personal website or
institutional repository. Authors requiring further information
regarding Elsevier’s archiving and manuscript policies are
encouraged to visit:
http://www.elsevier.com/copyright
Author's personal copy
Materials Letters 90 (2013) 138–141
Contents lists available at SciVerse ScienceDirect
Materials Letters
journal homepage: www.elsevier.com/locate/matlet
Copper sulfide nanorods grown at room temperature for
photovoltaic application
S.S. Dhasade a,b,c,n, J.S. Patil a,b,c, S.H. Han a, M.C. Rath b, V.J. Fulari c
a
Department of Chemistry, Hanyang University, South Korea
Radiation and Photochemistry Division, Bhabha Atomic Research Center, Mumbai 400 085, India
c
Holography and Material Research Laboratatory, Department of Physics, Shivaji University, Kolhapur 416 004, India
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 9 August 2012
Accepted 4 September 2012
Available online 12 September 2012
Copper sulfide nanorods with various diameters and lengths were obtained by the electrodeposition
method. Electrodeposition time can be used to control the diameter of the nanorods within the range of
30–35 nm. Electrodeposited copper sulfide thin films are grown at room temperature. Their structural,
morphological, optical properties, chemical composition and Raman laser spectrum are studied. The
room temperature films are utilized as a photocathode in photoelectrochemical (PEC) cell in 0.25 M
polysulfide electrolyte. The experimental results show that, the electrodeposited thin films allow
formation of light absorber, photosensitive, covellite copper sulfide.
& 2012 Elsevier B.V. All rights reserved.
Keywords:
Semiconductors
Chemical synthesis
X-ray diffraction
Electron microscopy
Optical properties
Photosensitivity
1. Introduction
Recently an interest has been focused on copper sulfide thin
films because of valence states and variations in stoichiometric
composition [1]. Different morphological patterns such as flowers,
distorted rods, spaghetti-like spherical microparticles nanorods,
wires, and long tube like patterns of copper sulfide crystals and
also long core copper sulfide nanowires have been successfully
synthesized [2–4]. Formation of copper sulfide thin films for
fabrication of nonporous heterojunction which is useful to convert sunlight into sustainable electricity [5]. Electrical conductivity and sensitive to ammonia of copper sulfide thin films are
reported [6,7]. Copper sulfide with different band gap energy
value from 2.40 eV to 2.80 eV, are also available [8–11]. The spray
pyrolysis method is used for the fabrication of CuS thin film these
films are conductive and photosensitive with band gap of 2.2 eV
[12]. Copper (I) Sulfide nanocrystals were synthesized for photovoltaic application [13–15]. Synthesis of nanowires, nanotubes
and nanovesicles of copper sulfide from nanoparticles by hydrothermal process is reported in the literature [16]. Unconventional
low-dimensional single-crystalline copper sulfide nanostructures
are also reported [17]. By using Cu nanowires as sacrificial templates
n
Correspondence to: Department of Physics, Vidnyan Mahavidyalaya, Sangola,
Ratnakunj Datta Nagar Vasud Road, Solapur, Maharashtra 413307, India.
Tel: þ91 9422652388.
E-mail address: [email protected] (S.S. Dhasade).
0167-577X/$ - see front matter & 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.matlet.2012.09.013
CuS nanotubes can be synthesized by a facile sacrificial templating
route [18]. Synthesis of various types of nanostructures of copper
sulfide is reported by a solvo-thermal reaction in ethylene glycol
[19,20]. According to literature survey it is seen that no reports are
available on synthesis of copper sulfide nanorods for photovoltaic
application by the electrodeposition method. In the present paper,
we report for the first time, photoelectrochemical performance of
CuS nanorods with diameter 30–35 nm and length of nanorods is
10–15 mm at room temperature by the electrodeposition method.
2. Experimental
2.1. Film growth
In the synthesis, equimolar (0.1 M) copper sulfide (CuSO4) and
sodium thiosulphate (Na2S2O3) are used as source of copper and
sulfur and 0.10 M triethanolamine is used as complexing agent.
Solutions are prepared in double distilled water. The ultrasonically
cleaned stainless steel and ITO substrate are used to prepare
samples. Copper sulfide thin films were prepared on stainless steel
and ITO substrate by electrodeposition technique. Electrolytic bath
contains 12 ml CuSO4 and 12 ml Na2S2O3 as sources of Cu and S
ions and 6 ml TEA as complexing agent with deposition time
of 15, 20, 25 and 30 min. Using Cyclic Voltammetry (CV), cyclic
voltammograms of aqueous acidic bath were scanned with a scan
rate of 50 mV/s using potentiostat (Princeton Perkin–Elmer,
Applied Research Versa-stat-II; Model 250/270) in three electrode
Author's personal copy
S.S. Dhasade et al. / Materials Letters 90 (2013) 138–141
30
40
50
60
2θ (Degree)
(208)
(a) 15 min
(206)
(b) 20 min
(108)
(116)
(c) 25 min
(106)
(008)
Intensity (A.U.)
(d) 30 min
70
80
Fig. 1. XRD patterns of CuS thin films deposited with (a) 15 min, (b) 20 min,
(c) 25 min and (d) 30 min for bath conc. of 0.10 M.
configuration. The reference electrode was a Saturated Calomel
Electrode (SCE). Deposition potential was determined by Cyclic
Voltammetry (CV) for a thin film material deposition. Orange
colored Cu layer deposited on the substrate at reduction potential
0.65 V. The film deposited at reduction potential 0.6 V gives
blackish sulfur layer. The electrodeposition of CuS thin films were
carried out at the deposition potential 0.7 V/SCE gives greenish
CuS film. After deposition the films were washed with double
distilled water and prepared in desiccators to avoid the oxidation.
Preparative parameters such as deposition time and concentration
of precursor were optimized.
3. Results and discussion
3.1. X-ray diffraction
The XRD pattern of the as-prepared CuS samples for bath
concentrations 0.10 M and with deposition time of 15, 20, 25 and
30 min are shown in Fig. 1(a–d).Various deposition time indicate
the formation of polycrystalline CuS. The phases of copper sulfide
can be easily distinguished by the powder X-ray diffraction
pattern, all of the peaks can be indexed as (106), (008), (108),
(116),(206) and (208) in the hexagonal CuS structure. We conclude that the films are composed of the reported hexagonal CuS
(JCPDS Card nos. 85-0620, with a ¼3.8020, 3.792 Å). Hence, the
copper sulfides present in the structure of the nanorods are
covellite (CuS). All of the samples show similar XRD pattern, it
means growth of the film is in a particular direction. Diffraction
peaks of other phases or impurities were not detected, further
confirming that the precursors have been completely transformed
into CuS nanostructures. The growth of an electrodeposit from an
electrolyte involves a phase transformation from ionic species in
the solution to a solid phase on the electrode. This phase
transformation is the cumulative effect of ionic transport, discharge, nucleation, and growth.
139
diameter from 10 nm to 20 nm. This happens because TEA acted
as linker. This provided hydrogen bonding and metal-ligand
bonding interaction with the facets of CuS crystals and resulting
in the formation of such a CuS nanorods. These CuS nanorods
were due to cumulative effect of ionic transport, discharge,
nucleation and growth at higher deposition time. These bundles
of nanorods are uniformly distributed over smooth homogenous
background. The well developed and matured CuS hexagonal
nanorod growths were shown in Fig. 2(b and c) with different
deposition time. Firstly, homogeneous mixture of the CuSO4:
(C6H15NO3)n was synthesized in distilled water, which acted as
the sacrificial template [21]. In the electrodeposition process, they
partly reacted with Na2S2O3 to form a Cu:(C6H15NO3)n@S core–
shell structure. This process can be described as follows: there
were several Cu2 þ ions ionized from CuSO4 that were located
around the surface of the Cu nanorods. At the initial stage of the
reaction, they reacted with S2 in the solution to form CuS belts.
Then, the Cu nanorods were covered with a very thin layer of CuS.
With the reaction proceeding, the outside shell of CuS was
gradually formed and the next layer starts reacting once the
CuS in the surface of the crystals got peeled off to the solution
after electrodeposition process ran for 25 min, as shown from the
SEM image of Fig. 2(c).
3.3. Optical properties
The optical band gap energy was determined from the plot of
(ahn)2 versus photon energy in the visible region as shown in
Fig. 3(a–d) for bath concentrations 0.10 M and deposition time of
15, 20 25 and 30 min. Band gap energy was calculated from the
classical relation for direct-band optical absorption. The optical
band gap of CuS films estimated from the Fig. 3(a–d) is 2.05 eV for
15 min deposition time, 2.29 eV for 20 min deposition time,
2.63 eV for 25 min deposition time and decreases with further
increase in deposition time of 30 min, these optical band gap
values are nearly equal with reported values [8–12]. The change
in the band gap with size of rods (surface morphology) shows the
blue shift in copper sulfide nanorods which can be attributed to
the formation of growth structure of copper sulfide thin films. The
increase in the optical band gap energy and appearance of second
band gap with deposition time implies the creation of additional
energy levels. The compositional analysis of CuS with deposition
time of 25 min was confirmed by energy-dispersive X-ray analysis, from the graph it is noted that the atomic percentage of
copper is 53.32 and while that of sulfur is 46.68. From atomic
percentage, copper to sulfur is of 1:1 ratio. Laser Raman spectroscopy is also an effective and suitable method for exploring the
surface layer structure of thin films. A Raman shift of sample is
detected at almost the wave numbers 435, 475, 499, 545 cm 1
respectively. The shift at wave number values [13–14] may be
linked with the vacancies in the CuS lattice, induced during the
film growth. The high intensity peaks recorded at 475 cm 1 can
be attributed to the formation of hexagonal CuS, by correlation
with the XRD and reported value.
3.4. Photoelectrochemical (PEC) studies
3.2. Scanning electron microscopy
SEM images with different deposition time revealing the
general morphology of the as-synthesized nanorods. These SEM
images of CuS thin film with bath conc. of 0.10 M and deposition
times of 15, 20, 25, and 30 min are shown in Fig. 2(a–d). From the
SEM images Fig. 2(a–d) it is seen that for lower deposition time
(15 min) of sulfur, hexagonal crystal structures are observed. At
higher deposition time (20 min and 25 min) of sulfur these
hexagonal crystals are converted in nanorods of different
The room temperature films are utilized as a photocathode in
photoelectrochemical (PEC) cell in 0.25 M polysulfide electrolyte.
Fig. 4 shows I–V curves of the photovoltaic performance of CuS
nanocrystals. At room temperature, current density against voltage characteristics of the photovoltaic device under zero illumination is shown by black curve and standard illumination is
shown by red curve, with irradiated light of 60 mW/cm2, showing
a power conversion efficiency of 0.69%. For preparing solid-state
devices photoelectrochemical characterization was chosen, which
Author's personal copy
140
S.S. Dhasade et al. / Materials Letters 90 (2013) 138–141
Fig. 2. SEM images of CuS thin films deposited with (a) 15 min, (b) 20 min, (c) 25 min and (d) 30 min for bath conc. of 0.10 M.
0.5
(a) Band gap =2.05eV
(b) Band gap =2.29eV
(c) Band gap =2.63eV
(d) Band gap =2.49eV
4
(a)
0.4
Current density(mA/cm2)
2
2
(αhν) (eV/cm) x10 9
0.6
(b)
(c)
(d)
0.3
0.2
0.1
3
2
1
0
dark
-1
-2
-3
0.0
1.5
2.0
2.5
hν (eV)
3.0
3.5
Fig. 3. Optical band gap energy of CuS thin film deposited with (a) 15 min,
(b) 20 min, (c) 25 min and (d) 30 min for bath conc. of 0.10 M.
it allows for a nondestructive and rapid evaluation of photoactivity of the CuS thin films, electrical shorting is also eliminated. The
polysulfide electrolyte is served as the redox mediator. The anodic
photocurrent increased gradually with increasing negative potential, indicating that the thin films were p-type [22]. The values of
short circuit current (Isc) and open circuit voltage (Voc) as
0.75 mA/cm2 and 675 mV respectively have been obtained under
the illumination intensity of 60 mW/cm2. The photoconversion
efficiency of 0.69% with fill factors of 21% is achieved. The
photoelectrochemical measurement confirmed good photoactivity of electrodeposited CuS thin films at room temperature. By
thermal, chemical and photoelectrochemical surface treatments
conversion efficiency of such film can be increased [23].
light
-4
0
-500
-1000
-1500
Voltage (mV/SCE)
Fig. 4. I–V curves showing the photovoltaic performance of CuS nanocrystals with
deposition time of 25 min and for bath conc. of 0.10 M. (For interpretation of the
references to color in this figure, the reader is referred to the web version of this
article.)
4. Conclusions
X-ray studies showed that the deposited films are polycrystalline in nature. Surface morphology shows that grains are hexagonal, with increase in deposition time they turn into hexagonal
nanorods. The electrodeposition method is constructive for preparation of large area CuS nanorods for PEC cells at the expense
of small amount of initial ingredients.The optical properties of
such films make them suitable for solar control coatings and
Author's personal copy
S.S. Dhasade et al. / Materials Letters 90 (2013) 138–141
photovoltaic devices. PEC performance can motivate to check its
feasibility in DSSC’s devices.
References
[1] Xuchuan J, Xie Y, Lu J, Wei H, Liying Z, Yitai QJ. Mater Chem 2000;10:2193.
[2] Gorai S, Ganguli D, Chaudhuri SJ. Cryst Growth Des 2005;5:875.
[3] Gao L, Wang E, Lian S, Kang Z, Lan Y, Di Wu. Solid State Commun
2004;130:309.
[4] Liao X, Chen N, Xu S, Yang S, Zhu J. J Cryst Growth 2003;252:593.
[5] Reijnen L, Meester B, Goossens A, Schoonman. J. Chem Vapor Deposition
2003;9:15.
[6] Erokhina S, Erokhin V, Nicolini C, Sbrana F, Ricci D, di Zitti E. Langmuir
2003;19:766.
[7] Setkusa A, Galdikasa A, Mironasa A, Simkienea I, Ancutieneb I, Janickisb V,
Kaciulisc S, Mattognoc G, Ingoc G. Thin Solid Films 2001;391:275.
[8] Grozdanov I, Najdoski M. J Solid State Chem 1995;114:469.
[9]
[10]
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18]
[19]
[20]
[21]
[22]
[23]
141
Sartale S, Lokhande C. Mater Chem Phys 2000;65:63.
Gadave K, Lokhande C. Thin Solid Films 1993;229:1.
Puspitasari I, Gujar T, Jung K, Joo Oh. Mater Sci Eng B 2007;140:199.
Nagcu C, Pop I, Ionescu V, Indrea E, Bratu I. Mater Lett 1997;32:73.
Page M, Niitsoo O, Itzhaik Y, Cahen D, Hodes G. Energy Environ Sci
2009;2:220.
Wu Y, Wadia C, Wanli M, Sadtler B, Alivisatos A. Nano Lett 2008;8:2551.
Ezema F, Hile D, Ezugwu S, Osuji R, Asogwa P. J Ovonic Res 2010;6:99.
Lu Q, Gao F, Zhao D. Nano Lett 2002;2:725.
Xu M, Wu H, Da P, Zhao D, Zheng G. Nanoscale 2012(4):1794.
Wu C, Yu Shu-Hong, Chen S, Liu G, Liu BJ. Mater Chem 2006;16:3326.
Wu C, Yu Shu-Hong, Antonietti M. Chem Mater 2006;18:3599.
Gong J, Yu Shu-Hong, Luo Qian HL, Liu X. Chem Mater 2006;18:2012.
Zhang L, Guang J, You H, Liu K, Yang M, Song Y, Zheng Y, Huang Y, Zhang H.
Inorg Chem 2010;49:3305.
Scragg J, Dale P, Peter L, Zoppi G, Forbes I. Phys Status Solidi B 2008; 245:
1772.
Damodar V, Damodar L. Mater Chem Phys 1998;56:45.