High Bending Durability of Efficient Flexible Perovskite Solar Cells Using Metal Oxide Electron Transport Layer

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1 Supporting information High Bending Durability of Efficient Flexible Perovskite Solar Cells Using Metal Oxide Electron Transport Layer Fengjiu Yang, Jiewei Liu, Hong En Lim, Yasuhisa Ishikura, Keisuke Shinokita, Yuhei Miyauchi, Atsushi Wakamiya, * Yasujiro Murata, and Kazunari Matsuda * Institute of Advanced Energy, Kyoto University, Uji, Kyoto , Japan Institute for Chemical Research, Kyoto University, Uji, Kyoto , Japan * wakamiya@scl.kyoto-u.ac.jp * matsuda@iae.kyoto-u.ac.jp Materials: All chemicals were used as received, without further purification. Tin oxide substrate (ITO, 1 Ω) and flexible PEN/ITO (1 Ω) were obtained from GEOMATEC and Oike Co., Ltd. nanoparticles (15 wt%) with a particle size of 1 15 nm in H 2 O colloidal dispersion were acquired from Alfa Aesar. Lead (II) iodide (PbI 2, 99.99%), Lead (II) bromide (PbBr 2, 99%), methylammonium bromide (MABr, > 98.%) formamidinium iodide (FAI, > 98.%), cesium iodide (CsI, 99.9%) and titanium diisopropoxide bis(acetylacetonate) (TiAcac) were purchased from Tokyo Chemical Industry Co., Ltd. Benzyl alcohol (99.8%) and TiCl 4 (99.%) were acquired from Sigma-Aldrich Co., Ltd. The solvent chemicals N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and chlorobenzene were dried before use. 2,2,7,7 -Tetrakis(N,N-di-p-methoxyphenylamino)-9,9 -spirobifluorene (spiro-ometad) was purchased from Merck Co., Ltd. Lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) salt powder, dehydrated ethanol, acetone, 2-propanol, other solvents were purchased from Wako Chemical Co., Ltd. and used as S1

2 received without no special treatment unless otherwise noted. Measurements: The all characterization and evaluation experiments were conducted in the ambient condition. The Cs 5 (MA.17 FA 3 ).95 Pb(I 3 Br.17 ) 3 perovskite film was loaded onto a glass substrate with a thickness of approximately 5 nm for the photoluminescence (PL) measurements; the fabrication processes of the perovskite layer were the same as those of the perovskite layers used in perovskite solar cells. An excitation with 532 nm wavelength and 75 W power were used for the steady-state PL spectroscopy of perovskite films. The optical absorption spectra of the perovskite films were recorded by a UV/Vis spectrophotometer (UV-18). The PL dynamics was measured by the time-resolved single-photon counting technique using a pulsed laser diode with a wavelength of 516 nm, a power of 1 nw, and a pulse width of 6.7 ns. Impedance spectroscopy was carried out under dark condition using electrochemical analyzer (ALS/HCH, 66 EAW) with a 5 mv AC amplitude, a frequency ranging from 1 khz to.1 Hz. The consecutive light soaking stability was characterized using a solar cell heat and weather resistibility test system (Bunkoukeihi, BIR-5P1) with a temperature control system. S2

3 Morphology of ITO, ITO/, and ITO/ substrates The and uniformly and fully covered the ITO substrates, as shown in the SEM images of Figure S1a-c. ITO ITO/ (c) ITO/ (d) ITO/ /perovskite Au spiro-ometad Perovskite ITO Figure S1. Surface SEM image of ITO substrate, ITO/, (c) ITO/, and (d) perovskite layer on the top of and cross sectional of based perovskite solar cells. Figure S1 F. Yang et al. /perovskite /perovskite 15 nm nm Figure S2. AFM image of ITO/ /perovskite, and perovskite layer on the top of. S3

4 -Z"( ) -Z"( ) Impedance spectroscopy of - and PSCs Impedance spectroscopy was conducted to understand the electrical characteristics of and ETMs in PSCs devices. Figure S3 shows the Nyquist plot of impedance in the - and -PSCs in the dark condition. The impedance spectra clearly show the similar shape between the - and -PSCs, however exhibits the differences in the radius of curves. The impedance spectra are divided into high- and low-frequency regions, where the high-frequency and low-frequency responses arise from the contribution of electron transport from the perovskite to the and and from the charge recombination process, respectively. 1 We found that the electron transport resistance (R ET ) of -PSCs evaluated from the arc radius in the high frequency region is smaller than that in -PSCs, because of the higher conductivity of. Interestingly, the recombination resistance (R REC ) of -PSCs also shows much high than that in the PSCs according to the larger arc radius in the lower frequency region, indicating that the higher photovoltaic performance of -PSCs is also supported by the results of impedance spectroscopy. x1 5 PSCs 8.x1 4 6.x1 4 4.x1 4 9.x1 5 6.x1 5 PSCs PSCs PSCs 2.x1 4 3.x1 5 1x1 5 2x1 5 3x1 5 4x1 5 Z'( ) 2.x1 4 4.x1 4 6.x1 4 8.x1 4 Z'( ) Figure S3. Nyquist plot of - and -PSCs measured in the dark condition. S4

5 Optical properties of flexible perovskite films We studied the charge carrier dynamics to clarify the charge extraction of and from the photoactive perovskite layer by optical absorption, steady-state photoluminescence (PL) and time-resolved PL (TRPL), the results are shown in the Figure S3a and S3b. Figure S3a shows the optical absorption spectrum of perovskite photo-active layer on the glass substrate. The absorption peak is located at 725 nm, which is blue-shifted as approximately 1 nm compared with the previously reported position. 2,3 The PL spectrum shows the peak at 75 nm, which is also blue-shifted as about 1 nm in comparison with the previously reported results. 2,3 The blue-shifted absorption and PL peak indicate the that the bandgap is larger than that previously reported for this perovskite photoactive layer and the higher V OC will be achieved. Moreover, the PL intensities of the perovskite films on and sharply decreased in comparison with that of the perovskite film on a glass. Notably, the decrease in PL intensity of the perovskite on the is much higher than that on, indicating that the charge extraction efficiency of is much higher than that of because of the lower conduction band and higher carrier mobility of. 4,5 The photoexcited carrier dynamics of perovskite layers were investigated using TRPL spectroscopy. Figure S3b shows the PL decay curves of perovskite, /perovskite and /perovskite. Faster PL decay is observed in the /perovskite than in the perovskite on the glass. The PL decay curves fitted using the double-exponential functions as solid lines well reproduce the experimental results. The obtained decay parameters are summarized in Table S2. The PL decay time of the perovskite layer significantly decreases from average values of 63.8 ns on the glass to 22.6 ns on the and 13.7 ns on the, which is consistent with the experimental results of PL intensity. The carrier extraction efficiency of is also confirmed to be higher than that of from the results of TRPL. 4-6 The physical reason for low charge extraction efficiency in is attributed to the shallower conduction band, lower carrier mobility, and interfacial defects between the perovskite and. 4,6 S5

6 Absorbance (a. u.) PL Normalized intensity (a. u.) Normalized PL instensity (a.u.) 1.5 Absorption Peorvskite /pero /pero Glass/perovskite Glass/ /perovskite Glass/ /perovskite IRF Wavelength (nm) Time (ns) Figure S4. Optical absorption and photoluminescence (PL) spectra of perovskite layers on glass, and. Time resolved PL decay profiles of perovskite films on the glass, and. The instrumental response function (IRF) is also shown. S6

7 Counts Counts Counts Counts Counts Counts Average J SC (ma/cm 2 ) : 21.1 : (d) Average J SC (ma/cm 2 ) J SC (ma/cm 2 ) Average V OC (V) : : 8 3 (e) J SC (ma/cm 2 ) 12 Average Voc (V) (c) Average FF (%) : : (f) V OC (V) Average FF (%) FF (%) FF (%) Figure S5 Histograms of the short-circuit current Figure density S5 F. (J Yang SC ), et al. open-circuit voltage (V OC ), and (c) the fill-factor (FF) in - and -PSCs (red: 35 -PSCs, black: 26 -PSCs). Histograms of (d) J SC, (e) V OC, and (f) FF in -fpscs (28 devices). S7

8 Normalized FF Normalized FF (c) Normalized J SC R 13.5 mm R 9 mm R 4 mm Normalized V OC R 13.5 mm R 9 mm R 4 mm R 13.5 mm R 9 mm R 4 mm Bending cycles (d) Bending cycles (e) Bending cycles (f) Normalized J SC R 9 mm R 4 mm Normalized V OC R 9 mm R 4 mm R 9 mm R 4 mm Bending cycles Bending cycles Bending cycles Figure S6. Bending stability tests.,, and (c) Normalized Figure J SC S5, V OC F. and Yang FF et of al. -fpscs during 4 bending cycles with various bending radii: 13.5, 9. and 4. mm. The average values from three different devices are plotted with error bars representing the standard deviation. (d), (e) and (f) Normalized J SC, V OC and FF as a function of the number of bending cycles at fixed radii of 9. and 4. mm for -fpscs during 2 bending cycles. The average values from three different devices are plotted with error bars representing the standard deviation. S8

9 R/R (%) Flexible PEN/ITO/ / perovskite/ spiro-ometad: before Flexible PEN/ITO/ / perovskite/ spiro-ometad: after (c) Flexible PSCs Au electrode: before (d) Flexible PSCs Au electrode: after Figure S7. and Surface morphology of spiro-ometad (flexible PEN/ITO/ /perovskite/spiro-ometad) before and after 4 bending test cycles under the R 9 bending condition, respectively. (c) and (d) Surface morphology of Au electrode (flexible PEN/ITO/ /perovskite/spiro-ometad/au) before and after 4 bending test cycles under R 9 condition, respectively ITO/PEN /ITO/PEN Bengding cycles Figure S8. Relative resistance change ( R/R ) of the ITO/PEN and ITO/PEN/ films as the function of bending cycles at bending radius of 9. mm. S9

10 Normalized FF Normalized FF Current density (ma/cm 2 ) Current density (ma/cm 2 ) PCE (%) Forward Reverse J SC V OC FF PCE Forward Reverse J V PCE 15.7% Voltage (V) Time (s) Figure S9. Photovoltaic performance of -fpscs with the highest V OC. J V curves of -fpscs with.1-cm 2 active area. Time evolution of an SPO PCE under MPP tracking of -fpscs under forward scanning conditions. Normalized J SC Flexible Normalized V OC Flexible Time (day) (c) Time (day) (d) Flexible Flexible Time (day) Time (day) Figure S1. Dark storage stability of rigid Figure substrate S8 TiO F. Yang 2 - and et SnO al. 2 -PSCs and -fpscs at room temperature and a relative humidity of 33.%, respectively. J SC, V OC, (c) FF and (d) PCE of - and -PSCs and -fpscs. S1

11 Normalized PCE Over 6% humidity Figure S11. Normalized PCE of - and - PSCs evaluated under continuous 1-Sun light soaking condition with high humidity of over 6% and temperature of ~ 25. C in ambient conditions. Both PSCs were not encapsulated. The recovery efficiencies were measured after the soaking measurement and storing at dark condition for 24 hours with a humidity of ~ 33.% Time (min) S11

12 Table S1. Surface roughness (root mean square value, RMS) of /perovskite, /perovskite and flexible ITO/ /perovskite layer, as measured by AFM. Sample (5 5 μm 2 ) Surface roughness (nm) /Perovskite 77.6 ± 6.3 /Perovskite 61.8 ± 4.7 Flexible ITO/ /Perovskite 71.2 ± 1.8 Table S2. Summary of time-resolved PL decay in perovskite, /perovskite and /perovskite on a rigid substrate. Parameters a, 1, 2, PL are amplitude ratio, decay constants of fast and slow components and the averaged PL decays, respectively. S1,S2 Sample a τ 1 (ns) τ 2 (ns) τ PL (ns) Perovskite 9±4 23.3± ± ±.3 /perovskite.79±1 6.9± 41.7± ±1.4 /perovskite.79±1 12.7± 6.7± ±.5 Table S3. Summary of the photovoltaic performance of -PSCs and -PSC. Scan directions J SC (ma/cm 2 ) V OC (V) FF (%) PCE (%) Reverse Forward Reverse Forward S12

13 Table S4. Summary of the photovoltaic performance of -fpscs during 2 times bending cycles. Bending cycles J SC (ma/cm 2 ) V OC (V) FF (%) PCE (%) R S (Ω cm 2 ) 19.8 ± ± 69.8 ± ± ± ± 1.15 ± ± 15.9 ±.3 1 ± ± ± ± ± ± ± ± ± ±.3 1 ± ± ± ± ±.3 1.5± ± ± 65.9 ± 14.8 ± ± 15 2 ± ± ± ± ± ± 1.1 ± ± ± ± ± ± 62.2 ± ± ± ± 9 ± 62. ± ± ± ±.1 8 ± 6 ± 13. ± 14.5 ± ± 8 ± ± ± ± ± 7 ± 58.4 ± ± 15.6 ± ±.1 7 ± 58.7 ± ± 15.4 ± Table S5. Summary of the degradation rate of fpscs in the storage condition. Structure Storage stability (%) Humidity (%) Time (h) Degradation rate(%/h) Ref. n-i-p PEN/ITO/ /Perovskite/spiro- OMeTAD/Au 97.9 ~ PEN/ITO/ZnO( )/MAPbI 3 /PTAA/Au ~ 8 (9) ~ 4 36 ~ 6 8 PEN/ITO/ED-TiO x /BK- +Perovskite/spiro-OMeTAD/Au 64 dry This work ITO/CPTA/MAPbI 3 /spiro-ometad/au 96 N 2 glovebox PET/ITO/NiO x (PEDOT:PSS)/MAPbI 3 /C 6 /Ag 85 () air p-i-n PEN/ITO/PEDOT:PSS/PEI.HI/MAPbI 3- xcl 3 -MAPbI 3 /PCBM/LiF/Ag <8 air 12 > PEN/ITO/CNT/ MAPbI 3 / SnO@CSCNT PET/ITO/Agmesh/PH1/PEDOT:PSS/MAPbI 3 /Al 9.5 N 2 glovebox S13

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