Tailoring of Electron Collecting Oxide Nano-Particulate Layer for Flexible Perovskite Solar Cells. Gajeong-Ro, Yuseong-Gu, Daejeon , Korea

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1 Supporting Information Tailoring of Electron Collecting Oxide Nano-Particulate Layer for Flexible Perovskite Solar Cells Seong Sik Shin 1,2,, Woon Seok Yang 1,3,, Eun Joo Yeom 1,4, Seon Joo Lee 1, Nam Joong Jeon 1 Young-Chang Joo 2, Ik Jae Park 2, Jun Hong Noh 1,* and Sang Il Seok 1,3,* 1 Division of Advanced Materials, Korea Research Institute of Chemical Technology, 4 Gajeong-Ro, Yuseong-Gu, Daejeon , Korea 2 Department of Materials Science and Engineering, Seoul National University, Seoul , Korea 3 School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), 50 UNIST-gil, Eonyang-eup, Ulju-gun, Ulsan , Korea. 4 Department of Energy Science, 2066 Seoburo, Jangan-gu, Sungkyunkwan University, Suwon , Republic of Korea These authors contributed equally to this work.

2 Experimental Synthesis of ZSO particles. All chemicals for the preparation of particles were of regent grade and were used without further purification. ZnCl 2 (12.8 mmol, Aldrich) and SnCl 4 5H 2 O (6.4 mmol, Aldrich) were dissolved in deionized water (160 ml) under vigorous magnetic stirring. N 2 H 4 H 2 O (N 2 H 4 /Zn molar ratio=12) was then added to the reaction solution. After 20 min of stirring, the mixture was transferred to titanium autoclave, which was kept at a temperature between 120 and 200 o C for 6 h in an electric oven. Then the autoclave was cooled to ambient temperature naturally. The resultant precipitates were centrifuged, washed with deionized water and ethanol and re-dispersed in 2 methoxy ethanol, resulting in a colloidal solution. The concentration of the colloidal solution is 12 mg/1ml. Solar cell fabrication. ZSO films were prepared by spin coating the colloidal dispersion of various-sized ZSO particles onto indium tin oxide (ITO) coated glass/poly ethylene naphthalate (PEN) substrate at 3000 rpm for 30 s. To control film thickness, the procedure was repeated 6 times without any dry processes. After baking at 100 C for 1 h in air, the perovskite layer was deposited onto the resulting ZSO film by a consecutive two-step spin coating process at 1000 and 5000 rpm for 10 s and 20 s, respectively, from the mixture solution of methylammonium iodide (CH 3 NH 3 I) and PbI 2. During the second spin coating step, the film was treated with toluene drop-casting, and then was dried on a hot plate at 100 C for 10 min. The detailed preparation of the CH 3 NH 3 I has been described in previous work 19. A solution of poly(triarylamine) (15 mg, PTAA, EM index, M n = 17,500 g mol -1 in toluene (1.5 ml) was mixed with 15 µl of a solution of lithium bistrifluoromethanesulphonimidate (170 mg) in acetonitrile (1 ml) and 7.5 µl 4-tertbutylpyridine. The resulting solution was spin-coated on the CH 3 NH 3 PbI 3 /Zn 2 SnO 4 thin film

3 at 3000 rpm for 30 s. Finally, an Au counterelectrode was deposited by thermal evaporation. The active area of the device is 0.16 cm 2 and the area for shadow mask is cm 2. Characterization. The crystal structure and phase of the materials was characterized using an X-ray powder diffractometer (XRD; New D8 Advance, Bruker). The morphologies and microstructures were investigated by field emission scanning electron microscopy (FESEM, SU 70, Hitachi). The optical properties of samples were characterized using a uv-vis spectrophotometer (UV 2550, Shimadzu). The J V curves were measured using a solar simulator (Oriel Class A, 91195A, Newport) with a source meter (Keithley 2420) at 100 mw cm 2, AM 1.5 G illumination, and a calibrated Si-reference cell certified by the NREL. The J- V curves were measured by reverse scan (forward bias (1.2 V) => short circuit (0V)) or forward scan (short circuit (0 V) => forward bias (1.2 V)). The step voltage and the delay time were fixed at 10 mv and 40 ms, respectively. The J V curves for all devices were measured by masking the active area with a metal mask cm 2 in area. Time-dependent PCE, dark current, impedance and capacitance voltage measurements were conducted with a potentiostat (PGSTAT302N, Autolab). Impedance measurements were carried out at DC bias of V = 0.1 V under 1 sun illumination with the frequency ranging between 1 MHz and 0.01 Hz. Capacitance voltage (CV) measurements were performed at fixed frequency (1 khz), employing the ITO/ZSO/perovskite/Au heterojunction structured devices. All measuremts were performed at room temperature.

4 Figure S1. TEM images of ZSO QD-1 (5.7 nm), QD-2 (9.3 nm) and NP (19.2 nm). 0.8 Intensity (a. u.) QD-1 QD-2 NP Figure S2. UV-vis absorption spectra of ZSO QD-1 (5.7 nm), QD-2 (9.3 nm) and NP (19.2 nm) Wavelength (nm)

5 Transmittance (%) Bare QD-1 QD-2 NP Wavelength (nm) Diffused reflectance (%) Figure S3. Transmittance and diffused reflectance spectra of ZSO films composed of QD-1 (5.7 nm), QD-2 (9.3 nm) and NP (19.2 nm) on ITO glass substrate. Figure S4. Average photovoltaic parameters for each 12 PSCs based on QD-1 (5.7 nm), QD- 2 (9.3 nm) and NP (19.2 nm) layer.

6 Figure S5. Cross-sectional SEM images of the PSC-based on a. QD-1 layer, b. QD-2 layer and c. NP layer Figure S6. Average photovoltaic parameters for each 12 designed ECLs based PSCs.

7 Figure S7. J-V curves of the PSC based on designed-zso-ecl/ch 3 NH 3 (I 0.9 Br 0.1 ) 3 measured by reverse scans with 10 mv voltage steps and 40 ms delay times under AM 1.5 G illumination. Figure S8. Stabilized PCE of the PSC based on designed-zso-ecl/ch 3 NH 3 (I 0.9 Br 0.1 ) 3 measured close to the maximum power point (~0.926 V).

8 Figure S9. J-V curves of the flexible PSC based on designed-zso-ecl/ch 3 NH 3 (I 0.9 Br 0.1 ) 3 measured by forward and reverse scans with 10 mv voltage steps and 40 ms delay times under AM 1.5 G illumination Counts 6 4 PCE (%) Figure S10. Histogram of solar cell efficiencies for the 24 designed ZSO ECL-based flexible PSCs

9 Table S1. Photovoltaic parameters of a flexible perovskite solar cell. J sc (ma/cm 2 ) V oc (V) FF η (%) Reverse Forward