Supplemental Material
Study on negative incident photon-to-electron conversion
efficiency of quantum-dot sensitized solar cells
Chunhui Li, Huijue Wu, Lifeng Zhu, Junyan Xiao, Yanhong Luo,
Dongmei Li, and Qingbo Menga)
Key Laboratory for Renewable Energy, Chinese Academy of Sciences, Beijing Key Laboratory for
New Energy Materials and Devices, Beijing National Laboratory for Condensed Matter Physics,
Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, P. R. China
a) Author
to whom correspondence should be addressed. Electronic mail: qbmeng@iphy.ac.cn.
Experimental details of QDSC fabrication
Mesoporous photoanode film preparation
TiO2 and SnO2 mesoporous films were prepared for loading QDs respectively. F-doped SnO2
(FTO) glasses (Nippon Sheet Glass; sheet resistance: 15Ω/square) were used for preparing both
photoanodes and counter electrodes. The preparation method of TiO2 film was similar to most
published procedures.1 A double layer structure was applied: a 13 μm thick transparent layer of 20
nm TiO2 adding a 5 μm thick scattering layer of 300 nm TiO2. The screen-printed TiO2
photoanode film was annealed at 450 oC for 30 min in air. The preparation method of SnO2 films
was almost the same as one of our previous work.2 10μm thick SnO2 film was deposited on FTO
glass by the screen-printing method and then annealed at 500 oC for 30 min in air. For both TiO2
and SnO2 films, TiCl4 treatment was carried out by dipping the film in 40 mM TiCl4 aqueous
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solution at 70 oC for 40 min. Finally the films were annealed at 500 oC for 30 min in air.
QDs sensitization
Two kinds of QDs, CdS and PbS, were assembled on the photoanode film. The successive ionic
layer adsorption and reaction (SILAR) technique was employed to assemble CdS QDs.3 The
photoanode film was dipped into 0.1 M Cd(NO3)2·4H2O methanol solution for 1 min, thoroughly
rinsed with methanol, then dipped into 0.1 M Na2S·9H2O methanol-water (1:1, v/v ) solution for
another 1 min, thoroughly rinsed with methanol, which was defined as one SILAR cycle.
Photoanodes sensitized with 5 cycles, 10 cycles, 15 cycles, and 20 cycles were prepared and
denoted as 5CdS, 10CdS, 15CdS, and 20CdS, respectively. For PbS sensitized photoanode, the
SILAR and chemical bath deposition (CBD) techniques were employed to assemble PbS and CdS
QDs, respectively.2, 4 The photoanode film was dipped into 0.02 M Na2S·9H2O aqueous solution
for 30 s, thoroughly rinsed with water, then dipped into 0.02 M Pb(NO3)2 aqueous solution for
another 30 s, thoroughly rinsed with water. Here, three SILAR cycles were carried out for PbS
deposition. Subsequently, CdS was deposited on PbS sensitized films by CBD method at 10 oC for
1 h. Finally, all the QDs sensitized photoanodes were passivated with ZnS by twice dipping into
0.1 M Zn(CH3COO)2·2H2O and 0.1 M Na2S·9H2O aqueous solution for 1 min alternately.
Counter electrode preparation
Cu2S and PbS counter electrodes were applied respectively. 4 μm thick Cu2S counter electrode
was prepared on FTO glass by screen-printing a Cu2S paste.5 For PbS counter electrode
preparation, FTO mesoporous film was first fabricated on FTO glass by screen-printing a FTO
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nanoparticle paste. PbS QDs were subsequently assembled on the FTO film by the following
SILAR procedure which was somewhat different from that used for sensitizing PbS QDs on
photoanode. The FTO film was dipped into 0.1 M Pb(NO3)2 aqueous solution for 30 s, thoroughly
rinsed with water, then dipped into 0.1 M Na2S·9H2O aqueous solution for another 30 s,
thoroughly rinsed with water. This SILAR cycle was repeated four times to complete the PbS
counter electrode preparation.
QDSC fabrication
Finally, the sensitized photoanode and counter electrode were sealed together with ethylene-vinyl
acetate (EVA) copolymer thin film under hot press. The polysulfide electrolyte was filled from a
hole previously made on the counter electrode, which was subsequently sealed by EVA film and a
cover glass. The standard polysulfide electrolyte used here was1 M Na2S and 1 M S in aqueous
solution. The fabricated QDSCs are labeled for distinguishment. For example, TiO2/10CdS-Cu2S
represents a QDSC whose photoanode is TiO2 film sensitized with 10 CdS SILAR cycles and
counter electrode is Cu2S.
REFERENCES
1
C. Li, Y. Luo, X. Guo, D. Li, J. Mi, L. Sø, P. Hald, Q. Meng and B. B. Iversen, J. Solid State Chem. 196, 504
(2012).
2
Q. Huang, F. Li, Y. Gong, J. Luo, S. Yang, Y. Luo, D. Li, X. Bai and Q. Meng, J. Phys. Chem. C 117, 10965
(2013).
3
C. Li, L. Yang, J. Xiao, Y. C. Wu, M. Søndergaard, Y. Luo, D. Li, Q. Meng and B. B. Iversen, Phys. Chem.
Chem. Phys. 15, 8710 (2013).
4
Q. Zhang, X. Guo, X. Huang, S. Huang, D. Li, Y. Luo, Q. Shen, T. Toyoda and Q. Meng, Phys. Chem.
Chem. Phys. 13, 4659 (2011).
5
M. Deng, S. Huang, Q. Zhang, D. Li, Y. Luo, Q. Shen, T. Toyoda and Q. Meng, Chem. Lett. 39, 1168
(2010).
3
FIG. S1. (a) IPCE spectra of SnO2/PbS-Cu2S QDSC measured by DC method. (b) The
corresponding Isc. The phenomenon of negative IPCE values also appears in the long wavelength
region.
FIG. S2. The light intensity distribution of Xenon lamp.
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FIG. S3. Time response of Isc for SnO2/PbS-Cu2S QDSC QDSC in the long wavelength region.
The monochromatic light illumination of different wavelengths is switched on at t = 0.
As shown in Fig. S3, the Isc background signal of SnO2/PbS-Cu2S QDSC is negative in the
dark. After the monochromatic light illumination of 1100 nm is switched on, there is no obvious
photocurrent signal observed. Although obvious photocurrent signal appears at 800 nm, the
photocurrent signal adding Isc background signal is still below zero and the apparent IPCE value
will be calculated negative. As the photocurrent response of SnO2/PbS-Cu2S QDSC becomes
stronger, and Isc rises near zero at 700 nm and above zero at 650 nm.
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