Supplementary Information
Quantum-Dot-Sensitized Solar Cell with Unprecedentedly High
Photocurrent
Jin-Wook Lee1, Dae-Yong Son1, Tae Kyu Ahn1, Hee-Won Shin1, In Young Kim2, Seong-Ju Hwang2,
Min Jae Ko3, Soohwan Sul4, Hyouksoo Han4 and Nam-Gyu Park1*
1
Department of Energy Science, School of Chemical Engineering, Sungkyunkwan University, Suwon
440-746, Korea, 2Center for Intelligent Nano-Bio Materials (CINBM), Department of Chemistry and
Nano Sciences, Ewha Womans University, Seoul 120-750, Korea, 3Photo-Electronic Hybrids Research
Center, Korea Institute of Science and Technology (KIST), Seoul 136-791, Korea, 4Center for
Computer Simulation and Analytical Science, Samsung Advanced Institute of Technology (SAIT),
Yongin 446-712, Korea
1
Figure S1 | XANES spectra of PbS, PbS:Hg QD adsorbed on TiO2 and references. X-ray
absorption near edge spectra (XANES) of (a) Pb L3 edge and (b) Hg L3 edge for PbS:Hg QDs
adsorbed on nanocrystalline TiO2 surface. PbS, HgS, PbO2, PbO, Pb(NO2)3 and HgCl2 powder were
also measured as a reference. PbS powder was prepared by drying the mixture of aqueous 0.1 M
Pb(NO3)2 and 0.1 M Na2S solution at 60 oC vacuum while HgS powder was prepared by drying the
mixture of aqueous 0.1 M HgCl2 and 0.1 M Na2S solution at 60 oC vacuum. Other reference chemicals
are purchased from Sigma-Aldrich.
Figure S2 | XPS analysis of PbS and PbS:Hg QDs adsorbed on TiO2. X-ray photoelectron spectra
(XPS) of (a) Pb 4f peaks and (b) Hg 4f peaks for PbS and PbS:Hg QDs adsorbed on nanocrystalline
TiO2 surface. HgS powder was also measured as a reference. HgS powder was prepared by drying the
mixture of aqueous 0.1 M HgCl2 and 0.1 M Na2S solution at 60 oC vacuum.
2
Table S1 | Stoichiometric ratio of mercury ion to lead and mercury ions in PbS:Hg QD, calculated from
the integrated area of Pb 4f and Hg 4f peaks in XPS measurement (Figure S3). Hg doping
concentration (at%) = SHg4f / (SPb4f + SHg4f), where SHg4f and SPb4f represent Hg 4f peak area and Pb 4f
peak area, respectively. Atomic sensitivity factors (6.7 for Pb 4f and 5.5 for Hg 4f) were reflected by
dividing each peak area by the atomic sensitivity factor. Removal of background signal and integration
of peak was conducted using VGX900-W system.
HgCl2 concentration
Hg doping concentration (at%)
0 mmol
0
2 mmol
5.4
4 mmol
6.3
6 mmol
14.6
8 mmol
16.7
Figure S3 | UV-visible absorption and transmission spectra of PbS and PbS:Hg QDs adsorbed
on TiO2. (a) UV-visible absorption and (b) transmission spectra of PbS and PbS:Hg QDs adsorbed on
nanocrystalline TiO2 surface. Inset of (a) shows absorbance at NIR region. The samples with
FTO/TiO2/QD/ZnS structures were prepared for measurement and a FTO/TiO2/ZnS sample was used
as a blank. The thickness of TiO2 layer was adjusted to 10.1 ± 0.2 μm.
3
Figure S4 | TEM micrographs of PbS and PbS:Hg QDs adsorbed on TiO2. TEM micrographs and
size distribution histograms of PbS:Hg QDs adsorbed on nanocrystalline TiO2 surface with different
HgCl2 concentration of (a) 0 mmol (b) 2 mmol (c) 4 mmol (d) 6 mmol and (e) 8 mmol. (f) QD size as a
function of HgCl2 concentration. Insets of (a)~(e) show magnified TEM image.
4
Table S2 | Resistivity, Hall coefficient, conductivity type, carrier density and hall mobility of PbS:Hg thin
film using hall effect measurement system. The measurement conducted at room temperature under
bias current of 3 μA and applied field was adjusted from 1 to 5 kG.
Field
[G]
Resistivity
[ohm∙cm]
Hall Coefficient
[cm3/C]
Type
Carrier Density
[1/cm3]
Hall Mobility
[cm2/(V∙s)]
1000
10.381
13.631
p
4.5794×1017
1.3140
2000
10.376
15.034
p
4.1520×1017
1.4492
3000
10.367
10.600
p
5.8886×1017
1.0218
4000
10.353
15.711
p
3.9732×1017
1.5144
5000
10.336
12.785
p
4.8825×1017
1.2324
5
Figure S5 | Photovoltaic performance of PbS and PbS:Hg QD-sensitized solar cell as a function
of coating cycle number. J-V curves of PbS:Hg QD-sensitized solar cells depending on the number of
coating cycle for (a) 0 mmol (b) 2 mmol (c) 4 mmol (d) 6 mmol and (e) 8 mmol HgCl2 in cationic
precursor solution. Thickness of TiO2 layer was adjusted to 6.5 ± 0.2 μm and polysulfide redox
electrolyte was composed of 1 M Na2S, 1 M S and 0.1 M NaOH in DI water.
6
Table S3 | Photovoltaic parameters of PbS:Hg QD-sensitized solar cells depending on the number of
coating cycle for each HgCl2 concentration. Thickness of TiO2 layer was adjusted to 6.5 ± 0.2 μm and
polysulfide redox electrolyte was composed of 1 M Na2S, 1 M S and 0.1 M NaOH in DI water. The
measurement was carried out under simulated one sun (100 mW/cm2)
Device ID
2
Jsc (mA/cm )
Voc (V)
FF (%)
2
Efficiency (%)
Area (cm )
0 mmol
2 cycle
8.20
0.348
47.66
1.36
0.482
4 cycle
8.46
0.314
47.86
1.27
0.464
6 cycle
6.54
0.280
46.42
0.85
0.426
2 mmol
2 cycle
10.04
0.411
48.29
1.99
0.475
4 cycle
16.47
0.393
42.80
2.77
0.422
6 cycle
17.53
0.381
41.10
2.75
0.487
4 mmol
2 cycle
10.07
0.436
47.14
2.07
0.461
4 cycle
15.90
0.422
41.08
2.75
0.479
6 cycle
18.64
0.395
36.69
2.70
0.456
6 mmol
2 cycle
4.84
0.438
58.86
1.25
0.415
4 cycle
9.64
0.443
44.66
1.91
0.459
6 cycle
15.71
0.419
42.58
2.80
0.435
8 cycle
15.81
0.406
42.12
2.70
0.417
8 mmol
4 cycle
9.04
0.399
43.27
1.56
0.424
6 cycle
14.34
0.403
42.91
2.48
0.438
8 cycle
13.77
0.401
39.67
2.19
0.476
7
Figure S6 | Effect of coating cycle number on photovoltaic performance. Effect of coating cycle
number on (a) power conversion efficiency and (b) short-circuit current density (JSC). Power conversion
efficiency and short-circuit current density are taken from Table S3.
Table S4 | Effect of HgCl2 concentration on photovoltaic parameters of the PbS:Hg QD-sensitized solar
cells. Thickness of TiO2 layer was adjusted to 10.1 ± 0.1 μm and polysulfide redox electrolyte was
composed of 1 M Na2S and 1 M S in DI water. The measurement was carried out under simulated one
sun (100 mW/cm2). The coating cycle number was 2 for 0 mmol, 4 for both 2 mmol and 4 mmol and 6
for both 6 mmol and 8 mmol HgCl2.
HgCl2
concentration
JSC (mA/cm )
VOC (V)
FF (%)
Efficiency (%)
Area (cm )
0 mmol
13.68
0.387
44.94
2.38
0.494
2 mmol
22.27
0.393
43.13
3.78
0.448
4 mmol
21.40
0.419
42.64
3.83
0.489
6 mmol
22.91
0.426
39.77
3.88
0.499
8 mmol
20.66
0.424
40.39
3.53
0.454
2
2
8
Figure S7 | Effect of coating cycle number on absorption spectra. UV-visible absorption spectra of
pristine PbS and PbS:Hg QDs adsorbed on nanocrystalline TiO2 surface for (a) 0 mmol HgCl2 and (b) 6
mmol HgCl2. Numbers in figures denotes the number of coating cycle. Thickness of TiO2 was adjusted
to 10.1 μm, and the same thickness of bare TiO2 was used as a blank.
9
Figure S8 | Effect of thickness on photovoltaic performance. (a) J-V curves and (b) EQE spectra
of PbS:Hg QD-sensitized solar cells as a function of TiO2 film thickness. 6 mmol of HgCl2 was used and
the number of coating cycle was 6. Polysulfide electrolyte was composed of 1 M Na2S and 1 M S in DI
water.
Table S5 | Effect of TiO2 thickness on photovoltaic parameters of PbS:Hg QD-sensitized solar cells. 6
mmol of HgCl2 was used and the number of coating cycle was 6. Polysulfide electrolyte was composed
of 1 M Na2S and 1 M S in DI water. The measurement was carried out under simulated one sun (100
mW/cm2).
2
VOC (V) FF (%)
TiO2 film thickness
JSC (mA/cm )
4.8 µm
11.22
0.414
5.8 µm
13.13
7.9 µm
2
Efficiency (%)
Area (cm )
41.12
1.91
0.470
0.409
40.73
2.19
0.440
19.53
0.409
43.04
3.44
0.458
10.5 µm
23.03
0.401
39.65
3.66
0.470
12.8 µm
24.67
0.390
36.51
3.51
0.475
10
Table S6 | Fitted time components and amplitudes for transient absorption signal for PbS and PbS:Hg
QDs adsorbed on nanocrystalline TiO2 surface using eqs 1 and 2 in the text. TiO2-QD composites on
FTO glass are prepared using same procedure used in photovoltaic performance measurement (Fig.
2b and Table S5), where thickness of TiO2 layer was 5 μm. (r=rise and d=decay component)
HgCl2
r (ps)
A1 (%)
1 (ps)
A2 (%)
2 (ps)
A3 (%)
3 (ps)
<d>
0 mmol
0.34
80
0.406
13
2.58
7
160
151
2 mmol
0.32
77
0.421
12
2.76
11
170
164
4 mmol
0.30
70
0.462
13
3.05
17
180
176
6 mmol
0.29
56
0.611
18
3.75
26
186
182
8 mmol
0.27
50
0.668
19
4.71
31
190
186
Concentration
Figure S9 | Shunt and series resistances. (a) Shunt and (b) series resistances as a function of
thickness and (c) shunt and (d) series resistances as a function of number of coating cycle. For (a) and
(b), HgCl2 concentration was 6 mmol and number of coating cycle was 6. For (c) and (d), the thickness
of TiO2 was ca. 6.5 μm ± 0.2 and HgCl2 concentration was 6 mmol. Shunt and series resistance were
calculated using K2400 I-V program based on LABVIEW (PV Measurements Inc).
11
Figure S10 | Effect of CsOH additive in electrolyte. (a) Effect of CsOH concentration in polysulfide
electrolyte (1 M Na2S, 1 M S in DI water) on (a) J-V curves of PbS:Hg QD-sensitized solar cells and (b)
dependence of fill factor on CsOH concentration. 6 mmol of HgCl2 was used and number of coating
cycle was 6. Thickness of TiO2 layer was 10.1 ± 0.2 μm.
Table S7 | Effect of CsOH concentration in polysulfide electrolyte (1 M Na2S and 1 M S in DI water) on
photovoltaic parameters of PbS:Hg QD-sensitized solar cells. 6 mmol of HgCl2 was used and number
of coating cycle was 6. Thickness of TiO2 layer was 10.1 ± 0.2 μm and measurement was carried out
under simulated one sun (100 mW/cm2)
2
VOC (V) FF (%)
Concentration of CsOH (M)
JSC (mA/cm )
0
21.35
0.404
0.15
21.25
0.3
2
Efficiency (%)
Area (cm )
45.55
3.93
0.414
0.412
49.64
4.34
0.415
22.02
0.414
50.82
4.63
0.428
0.45
22.02
0.407
50.98
4.57
0.407
0.6
21.65
0.410
50.97
4.52
0.410
12