Supporting information:
Effect of Different Hole Transport Materials on Recombination
in CH3NH3PbI3 Perovskite Sensitized Mesoscopic Solar Cells
Dongqin Bi, Lei Yang, Gerrit Boschloo, Anders Hagfeldt and Erik M. J. Johansson*
Department of Chemistry-Ångström, Physical Chemistry, Uppsala University, Sweden.
Experimental
Materials synthesis. The perovskite sensitizer (CH3NH3)PbI3 was prepared according to the reported
procedure[23]. Generally, A hydroiodic acid (30 mL, 57 wt.% in water, Aldrich) was mixed with
methylamine (27.8 mL, 0.273 mol, 40% in methanol, TCI) at 0℃ for 2 h. The resulting solution was
evaporated and produced synthesized chemicals (CH3NH3I). To prepare (CH3NH3)PbI3, equal molar of
synthesized CH3NH3I and PbI2 were stirred in γ-butyrolactone at 60 ℃ for overnight.
Solar cell fabrication and characterization. Fluorine-doped tin oxide (F:SnO2) coated glass
(Pilkington TEC 15) 15 Ω/□ was patterned by etching with Zn powder and HCl diluted in distilled
water. The etched substrate was then cleaned with Acetone, ethanol and then dried in air. A compact
TiO2 blocking layer was first deposited onto the surface of a pre-cleaned FTO substrate by spray
pyrolysis on a hotplate at 450 ℃ using 0.2 M Ti-isopropoxide, 2 M acetylaceton in isopropanol. 0.5
µm thick mesoporous TiO2 layer was deposited by spin-coating TiO2 paste (Dyesol 18NR-T). The
layers were then sintered in air at 500 ºC for 30 minutes. In dry box, 40 wt% perovskite precursor
solution was dispensed onto the mesoporous electrode film spin-coating at 1500 RPM for 30 seconds.
The coated films were then placed on a hot plate set at 100ºC for 20 minutes in air. The prepared TiO2
films were coated with perovskite precursor solution, followed by heating at 100℃ for 15 min. The
composition
of
hole
transport
material
(HTM)
7,7′-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,99-spirobifluorene
was
0.170
(spiro-OMeTAD,
M
2,2′,
Merck),
20mg/ml P3HT, 500mM DEH (4-(Diethylamino)benzaldehyde diphenylhydrazone), 0.064 M
bis(trifluoromethane)sulfonimide
lithium
salt
(LiTFSI,
99.95%,
Aldrich)
and
0.198
M
4-tert-butylpyridine (TBP, 96%, Aldrich) in chlorobenzene (99.8%, Aldrich). The (CH3NH3)PbI3
sensitized TiO2 films were coated with HTM solution using spin-coating method at 4000 rpm. 200 nm
Ag electrodes is deposited onto the solar cell by thermal evaporation.
Current-voltage (J-V) characteristics were measured using a Keithley 2400 source/meter and a
Newport solar simulator (model 91160) giving light with AM 1.5 G spectral distribution, which was
calibrated using a certified reference solar cell (Fraunhofer ISE) to an intensity 1000 W/m2. A black
mask of 0.2 cm2 was applied on top of the cell to avoid significant additional contribution from light
falling on the device outside the active area.
Incident photon to current conversion efficiency (IPCE) spectra were recorded using a
computer-controlled setup consisting of a xenon light source (Spectral Products ASBXE-175), a
monochromator (Spectral Products CM110), and a potentiostat (EG&G PAR 273), calibrated using a
certified reference solar cell (Fraunhofer ISE). Electron lifetime and transport times were performed
using a white LED (Luxeon Star 1W) as the light source. Voltage and current traces were recorded
with a 16-bit resolution digital acquisition board (National Instruments) in combination with a current
amplifier (Stanford Research Systems SR570) and a custom-made system using electromagnetic
switches. Transport time and lifetimes were determined by monitoring photocurrent and photovoltage
transients at different light intensities upon applying a small square wave modulation to the base light
intensity. The electron lifetime measured with transient photovoltage was calculated using from the
following equation: Voc=Voc,0 + ∆V exp(-t/τ), where ∆V is the change in open-circuit voltage (Voc) due
to the modulated small change in light intensity, Voc,0 is the open-circuit voltage before the change in
light intensity, and τ is the electron lifetime. The photocurrent and photovoltaic responses were fitted
using first-order kinetics to obtain time constants.
Photo-induced absorption (PIA) spectra were recorded using a white probe light generated by a 20
W tungsten-halogen lamp which was superimposed with a square-wave modulated (on-off) blue LED
(Luxeon Star 1 W, Royal Blue, 460 nm) used for excitation. The transmitted probe light was focused
onto a monochrometer (Action Research Corporation SP-150) and detected by a UV enhanced silicon
photodiode connected to a current amplifier and lock-in amplifier (Stanford Research System models
RS570 and RS830, respectively). The intensity of approximately 6 mWcm-2 and a modulation
frequency of 9.3 Hz were used for the excitation LED.
Electrochemical measurement of DEH:
Cyclic voltammetry curve of DEH and ferrocene performed on a Ivium potentiostat with a
3-electrode set-up.. Glass carbon, grapheme and AgCl/Ag were used as working electrode, counter
electrode and reference electrode.The electrolyte solution contained 0.5mM DEH and 0.1M
LiClO4 in CH3CN.The setup was internally calibrated against the ferrocene/ferrrocenium redox
couple (Fc+/Fc). The scaning rate is 50mv/s.
Epa(V) vs AgCl/Ag
Ere(V)
E1/2(V)
Ferrocene
0.546
0.458
0.502
DEH
0.673
0.571
0.622