Supporting Information
Diluted-CdS QDs-assisted SnO2 Electron Transport Layer with Excellent
Conductivity and Suitable Band Alignment for High Performance Planar Perovskite Solar Cells
Zheng Lv1, Li He1, Haipeng Jiang1, Xiaojun Ma1, Fengyou Wang1, Lin Fan1, Maobin Wei1,
Jinghai Yang1, Lili Yang1*, Nannan Yang2*
1Key Laboratory of Functional Materials Physics and Chemistry of the Ministry of Education, Jilin Normal University, Changchun 130013, China
2College of Mechanical Engineering, JiLin Engineering Normal University, Changchun 130052, PR China
*To whom correspondence should be addressed.
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Materials. Methylammonium iodide (CH3NH3I) and PbI2 were purchased from
Xi’an Polymer Light Technology Corp. Spiro-OMeTAD, acetonitrile, 4-tert-butylpyridine, chlorobenzene, and Lithium ditrifluoromethane sulfimide were purchased from YOUXUAN Tech. Anhydrous dimethyl sulfoxide (DMSO), Anhydrous Dimethylformide (DMF), and Tin(IV) oxide, 15% in H2O colloidal
dispersion were purchased from Alfa Aesar. Linoleic Acid was obtained from TCI. Cadmium chloride hemi (pentahydrate) was obtained from Aladdin. Sodium sulfide nonahydrate and Sodium hydroxide were purchased from Sinopharm Chemical Reagent Corporation Co., Ltd.
Preparation of CdS QDs. CdS is synthesized by hydrothermal method. First, 5
ml aqueous solution containing 0.02 mol of sodium hydroxide was added to the mixture of 5 mL of linoleic acid and 15 mL of absolute ethyl alcohol, which was stirred for about 60 min. Then 7 mL of aqueous solution containing 0.5 g of CdCl2·2.5H2O and 8 mL of aqueous solution containing 0.213g of Na2S·9H2O were
added in order to the above mixture solution, which was stirred for about 20 min. After that, the mixture was transferred into a 50 mL Teflon autoclave, which was placed in drying heater for about 12 h at 180 °C. After the reaction, the autoclave was cooled down to room temperature. The yellow sediment in the autoclave was collected through the centrifugal, and washed with absolute ethyl alcohol by centrifugalization for several times and then dried at 70 °C for 12 h. The obtained products were dispersed in toluene to form a well-distributed ink with concentration of 0.01 g/mL.
Fabrication of solar cells. The 462 mg PbI2 /163 mg MAI was dissolved in a
Dimethyl sulfoxide (DMSO) and Dimethylformide (DMF) mixed solvent (v:v=3:7) to form precursor solution. The mixed solution (80μL) was spin-coated on the SnO2 and
diluted-CdS QDs assisted-SnO2 substrates by a consecutive two-step spin-coating
process at 1,000 and 4,000 rpm for 10 and 30 s. During the second step, 400 μL of chlorobenzene was added onto the substrate before the end of spinning process. The substrates were then annealed at 100 °C for 10 min in a nitrogen-filled glovebox to obtain the MAPbI3 films. After cooling down to room temperature, a volume of 80μL
of the hole-transporting material, which synthesized by 72 mg spiro-OMeTAD in 1 mL of chlorobenzene with addition of 28.5μL 4-tert-butylpyridine and 18.5 μL of Li-TFSI solution (520 mg in 1 mL acetonitrile), was spin-coated on the perovskite films at 3000 rpm for 30s. Finally, 100-nm-thick sliver counter electrode was deposited by thermal evaporation.
Characterizations. The scanning electron microscope (SEM) images were
measured using a Hitachi S-4800 equipped with an energy dispersive X-ray spectroscopy (EDS) system (EDAX Genesis 2000). The crystal structure of the perovskite was characterized by X-ray power diffraction (XRD) (Japan Rigaku D/max-ga X-ray diffractometer) using Cu Kg ( そ =0.15406 nm). The photocurrent density dependence on the voltage (J-V) were measured under AM 1.5 G simulated sunlight illumination (100 mW/cm2, Model 91160, Newport). The spectral response
was taken by an EQE measurement system (QEX10, PV Measurement), which is equipped with a monochromator, a lock-in amplifier, a Xe lamp, and a current-voltage
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amplifier. The optical properties of the films were analyzed using an UV-Vis-near-infrared (NIR) spectrophotometer (UV-3101PC). The photoluminescence (PL) spectra were obtained using a PL microscopic spectrometer (Fluorolog-3 spectrometer, Horiba Jobin Yvon, America) with a 405 nm CW laser excitation source. The time-resolved PL (TRPL) spectra (Fluorolog-3 spectrometer, Horiba Jobin Yvon, America) were measured by using an emission wavelength of 770 nm. X-ray photoelectron spectra (XPS) were conducted by the Thermo ESCALAB 250 measurement system.
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Table S1. Carrier concentration and Hall mobility of SnO2 and CdS(1.0%)-SnO2 ETL deposited
on FTO substrates.
Samples Carrier concentration(cm-3) Hall Mobility(cm2/V/s) Type
Pure SnO2 2.54×1016 7.34×102 n
Figure S2. Line graph of (a)Jsc, (b)Voc, (c)FF and (d)PCE via adding different volume ratio of
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Table S2. Key J–V parameters of PSCs based on SnO2 ETL with adding different volume ratio of
CdS QDs.
Device Jsc (mA/cm2) Voc (V) FF (%) PCE (%)
Pure SnO2 21.70 1.10 76.51 18.27
CdS(0.5%)-SnO2 22.86 1.12 77.68 19.88
CdS(1.0%)-SnO2 23.45 1.13 78.42 20.78
CdS(1.5%)-SnO2 22.40 1.11 77.43 19.26
Table S3. Photovoltaic parameters of PSCs based on SnO2 ETLs.
Devices Jsc (mA/cm2) Voc (V) FF PCE (%)
1 21.02 1.11 77.68 18.12 2 21.24 1.11 77.94 18.37 3 21.45 1.08 74.56 17.40 4 20.60 1.09 77.49 17.46 5 19.47 1.06 77.22 16.03 6 21.38 1.08 77.86 17.96 7 20.59 1.11 74.67 17.20 8 21.55 1.11 77.77 18.69 9 21.31 1.10 78.06 18.15 10 22.15 1.08 72.89 17.45 11 21.66 1.07 77.25 17.90 12 20.99 1.12 78.36 18.49 13 19.91 1.08 76.84 16.51 14 20.88 1.09 77.09 17.63 15 21.32 1.08 76.52 17.62 16 21.08 1.09 76.91 17.67 17 20.78 1.07 77.53 17.23 18 20.95 1.09 77.57 17.71 19 21.22 1.08 77.53 17.77 20 21.54 1.08 75.16 17.48
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Table S4. Photovoltaic parameters of PSCs based on CdS(1.0%)-SnO2 ETLs.
Devices Jsc (mA /cm2) Voc (V) FF PCE (%)
1 22.63 1.11 77.65 19.51 2 21.89 1.09 76.02 18.14 3 22.66 1.10 77.81 19.39 4 21.65 1.11 77.16 18.54 5 22.55 1.10 77.64 19.26 6 22.20 1.13 77.91 19.54 7 21.56 1.12 77.78 18.78 8 22.27 1.09 78.64 19.09 9 22.15 1.13 77.32 19.35 10 22.75 1.10 76.99 19.27 11 22.82 1.13 78.05 20.13 12 22.31 1.12 77.65 19.40 13 22.05 1.12 77.86 19.23 14 23.45 1.13 78.42 20.78 15 22.74 1.12 78.25 19.92 16 22.76 1.13 76.86 19.77 17 22.90 1.12 77.06 19.76 18 22.54 1.07 75.75 18.27 19 22.50 1.09 78.14 19.16 20 22.30 1.12 75.80 18.93
Table S5. The fitted EIS data of the PSCs based on SnO2 and CdS(1.0%)-SnO2, respectively.
PSCs Rs (ohm) Rtr (ohm) Rrec (ohm)
SnO2 51.67 7614 3.339×105
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Table S6. Photovoltaic parameters of PSCs based on SnO2 and CdS(1.0%)-SnO2 ETLs without
any encapsulation stored at ambient condition(relative humidity of 40%, temperature of 23℃)
ETL Parameters 0 h 75 h 150 h 225 h 300 h 375 h 450 h 525 h 600 h Jsc(mA/cm2) 22.21 21.44 20.63 19.99 19.95 18.22 17.61 16.51 15.55 Voc(V) 1.10 1.10 1.09 1.07 1.08 1.07 1.07 1.06 1.05 FF 76.97 74.75 72.75 72.09 71.28 68.01 67.54 67.48 66.74 SnO2 PCE 18.81 17.62 16.35 15.44 15.35 13.26 12.72 11.81 10.90 Jsc(mA/cm2) 23.45 23.12 22.60 22.44 22.27 22.18 22.13 21.92 21.86 Voc(V) 1.13 1.12 1.12 1.12 1.11 1.11 1.11 1.11 1.10 FF 78.42 78.30 78.12 77.74 77.12 76.82 76.69 76.89 76.71 CdS(1.0 %)-SnO2 PCE 20.78 20.27 19.78 19.54 19.07 18.92 18.84 18.71 18.45
