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1 Electronic Supplementary Material (ESI) for Energy & Environmental Science. This journal is The Royal Society of Chemistry 0 Electronic Supplementary Information Slow surface passivation and crystal relaxation with additives to improve device performance and durability for tin-based perovskite solar cells Efat Jokar, 1 Cheng-Hsun Chien, 1 Amir Fathi, 1 Mohammad Rameez, 1 Chang-Yu Hao 1 and Eric Wei- Guang Diau 1, * 1 Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University, 01 Ta-Hsueh Rd., Hsinchu 300, Taiwan. Center for Emergent Functional Matter Science, National Chiao Tung University, 01 Ta-Hsueh Rd., Hsinchu 300, Taiwan; diau@mail.nctu.edu.tw Experimental section Materials Butylammonium Iodide (BAI): BAI was prepared through the reaction of butylamine and HI (57% in water) at molar ratio 1:1 in an ice bath. The obtained powder was washed with diethyl ether several times and dried in a vacuum oven overnight at 50 C. Ethylenediammonium Diiodide (EDAI ): Ethylenediamine and HI were reacted in an ice bath at molar ratio (:5). Excess HI was added to ensure complete reaction. A white powder precipitated in the flask; a powder was separated and washed with diethyl ether several times. The obtained powder was dried in a vacuum oven overnight at 50 C. Device Fabrication Cleaned glasses coated with indium tin oxide (ITO) were treated with an oxygen plasma for 0 min. A PEDOT:PSS layer was then spin-coated onto these substrates at 5000 rpm for 60 s and dried at 150 C for min. The films were transferred into a glovebox for the deposition of a perovskite layer (O ppm, H O 0.5 ppm). The reference FASnI 3 film was spin-coated from a precursor solution (FAI 1 M, SnI 1M, SnF 0.1 M, in DMSO) at 5000 rpm for 90 s ( µl of PSK solution on cm cm substrate). 1

2 Chlorobenzene (800 μl) was dropped after 60 s during the spin-coating. After spin coating the dark red film that represented the formation of the FASnI 3 -DMSO complex was annealed at 0 C for min. Deposition of PSK film was done under flow of nitrogen in glovebox to avoid the accumulation of solvent inside of spin-coater. The perovskite structure was modified on adding BAI or EDAI. FASnI 3 - xbai films were prepared under the same conditions as the standard; x is the molar fraction of BAI and EDAI that was added to the perovskite solutions. The perovskite solutions contained BAI (x = 0.1, 0.15, 0. and 0.5 M), FAI ((1 x) M), SnI (1 M) and SnF (0.1 M). For FASnI 3 -yedai films, the solutions contained EDAI (y = 0.01, 0.0 and 0.03 M), FAI ((1 y) M), SnI (1 M) and SnF (0.1 M). Afterwards, electron-transfer and hole-blocking layers were coated via thermal evaporation (pressure 5-6 Torr); C 60 0 nm, BCP 6 nm were deposited. The silver back-contact electrode (0 nm) was eventually deposited via thermal evaporation. Characterization of materials and devices A field-emission scanning electron microscope (FESEM, Hitachi SU80) was used to investigate the morphology of the samples. The X-ray diffraction (XRD) patterns of the thin films coated on the ITO substrates were acquired with an X-ray diffractometer. The current density-voltage characteristics of devices were recorded with a digital source meter (Keithley 400) under one-sun illumination (AM 1.5G, 0 mw cm - ) from a solar simulator (XES-40S1, SAN-E1) and were calibrated with a silicon diode and a KG-5 filter to decrease the mismatch of the spectrum. All measurements were done under ambient conditions. The inciden-photon-to- current (IPCE) spectra were recorded with a system comprising a Xe lamp (A-, PTi, 150 W) and a monochromator (PTi). The absorption spectra of the thin-film and solution samples were recorded with a spectrophotometer (JASCO V-570). The PL transients were recorded with a time-correlated single-photon-counting (TCSPC) system (Fluotime 00, PicoQuant) with excitation at 635 nm from a picosecond pulsed-diode laser (LDH-635, PicoQuant, FWHM ~70 ps). The repetition rate of the laser used for all experiments was 5 MHz; the pulse energy was 4 μj cm -. The PL temporal profiles were collected at 850±3 nm, which covers the emission maximum but is at the edge of the sensitive region of the used MCP-PMT (R3809U-50), for all perovskite samples under investigation. X-ray photoelectron spectra (XPS) were recorded (Thermo K-ALPHA Surface Analysis) for perovskite films coated on ITO substrates. The samples were etched with a beam of ions (1 kev Ar + ) for 0 s and 30 s. Given a possible drift of the spectra, the curves were corrected based on the C1s line at 84.6eV.The electrochemical impedance spectra (EIS) of all devices were measured with an

3 electrochemical workstation (IM 6, Zahner, Germany) over frequency range 0 mhz - 4 MHz with ac amplitude mv under darkness at 0.3 V. The obtained EIS data were fitted (Z-view software) based on an equivalent- circuit model. Capacitance-voltage (C-V) measurements were conducted on applying a perturbation mv of AC voltage at frequency 1 khz, which was superimposed on the DC bias to yield the final C-V curves. The depletion capacitance C normalized to the area is given by C = (V fb V) qεε 0 n in which V is the applied voltage, q corresponds to the elementary charge, ε is the relative permittivity of the FASnI 3, ε 0 denotes the permittivity of vacuum, n is the total concentration of acceptor impurities and V fb is the flat-band potential of the contact. The abscissa intercept of the linear regime in a Mott Schottky plot provided the built-in potential. The flat-band potential, V fb of a PSC is generally defined as the compensating energetic potential difference required between the quasi-fermi level of perovskite (E P ) and that of ETL/cathode electron-selective contact (E Fn ) and is expressed mathematically as V fb = E Fn E P As other parameters were identical for all fabricated PSC, any variation in flat-band potential could be attributed to the variation in the quasi-fermi level of perovskite. 3

4 (a) (b) (c) (d) Figure S1. SEM images of FASnI 3 with varied proportions of BAI additive: (a) %, (b) 15 %, (c) 0 % and (d) 5 % 4

5 Figure S. SEM images of FASnI 3 with varied proportions of EDAI additive: (a) 0%, (b) 0.5 %, (c) 1 %, (d) %, (e) 3 % and (f) 5 % 5

6 (a) (b) (c) Figure S3. AFM images of (a) FASnI 3, (b) FASnI 3 -BAI 15 % and (c) FASnI 3 -EDAI 1%. AFM was measured in air (RH = 50%) and oxidation of the films may occur to produce the white spots as shown in (a) and (b). 6

7 (a) 1.8 Absorbance Wavelength /nm FASnI 3 FASnI 3 -% BAI FASnI 3-15% BAI FASnI 3-0% BAI Absorbance (b) FASnI 3 FASnI 3-1% EDAI FASnI 3 - % EDAI FASnI 3-3% EDAI Wavelength /nm Figure S4. UV-vis absorption spectra of thin-film samples of (a) FASnI 3 -xbai and (b) FASnI 3 -yedai with varied proportions of x and y. 7

8 Figure S5. Side-view SEM images of typical devices made of (a) FASnI 3 -BAI 15 % and (b) FASnI 3 - EDAI 1 % samples 8

9 0 (a) Current Density /ma cm FASnI 3 FASnI3-% BAI FASnI3-15% BAI FASnI3-0% BAI FASnI3-5% BAI Voltage /V (b) 80 IPCE /% FASnI 3 BAI % BAI 15% BAI 0% BAI 5%.87(mA cm^-) (ma cm^-).5(ma cm^-) (ma cm^-) (ma cm^-) Wavelength /nm Intergated current Density /ma cm - Figure S6. (a) Current-voltage and (b) corresponding IPCE spectra with integrated current densities of the devices made of FASnI 3 -xbai samples 9

10 Voc /V FASnI3 BAI % BAI 15% BAI 0% Jsc /ma cm FASnI3 BAI % BAI 15% BAI 0% FF PCE /% FASnI3 BAI % BAI 15% BAI 0% 3.0 FASnI3 BAI % BAI 15% BAI 0% Figure S7. Statistical boxplots of photovoltaic parameters for PSC devices made of FASnI 3 -xbai samples that were fabricated under the same experimental conditions for all cells of each type

11 (a) 0 Current Density /ma cm Devices PCE /% FASnI EDAI 0.5% EDAI 1% 7.4 EDAI % 5.3 EDAI 3% Voltage /V FASnI 3 0.5% EDAI 1% EDAI % EDAI 3% EDAI (b) IPCE /% FASnI 3 FASnI 3-1% EDAI FASnI 3 -% EDAI 4.9 macm -.6 macm macm Wavelength /nm Intergated current Density /ma cm - Figure S8. (a) Current-voltage and (b) corresponding IPCE spectra with integrated current densities of the devices made of FASnI 3 -yedai samples 11

12 Voc /V Jsc /macm FASnI3 1% EDAI % EDAI 3% EDAI FASnI3 1% EDAI % EDAI 3% EDAI FF PCE /% FASnI3 1% EDAI % EDAI 3% EDAI 1 FASnI3 1% EDAI % EDAI 3% EDAI Figure S9. Statistical boxplots of photovoltaic parameters for PSC devices made of FASnI 3 -yedai samples that were fabricated under the same experimental conditions for all cells of each type 1

13 (a) Voc /V FASnI3 FASnI3-15% BAI FASnI3-1% EDAI (b) Jsc /ma cm FASnI3 FASnI3-15% BAI FASnI3-1% EDAI (c) FF FASnI3 FASnI3-15% BAI FASnI3-1% EDAI Figur e S. Statistical boxplots of (a) Voc, (b) Jsc and (c) FF for reference device FASnI 3 and for devices made with two additives at optimum proportions for 30 devices fabricated under the same experimental conditions for cells of each type 13

14 (a) 0 (b) 0 Current Density /ma cm Reverse Forward Current Density /ma cm Reverse Forward Voltage /V Voltage /V Figure S11. J V characteristics of (a) FASnI 3 -BAI 15 % and (b) FASnI 3 -EDAI 1 % devices with two scan directions: forward scan (from short circuit to open circuit) and reverse scan (from open circuit to short circuit) 14

15 FASnI 3 FASnI 3-15% BAI FASnI 3-1% EDAI 1.8 kt/q Voc /mv kt/q kt/q 0 0 Iight Intensity /W cm - Figure S1. Semi-logarithmic plots of the dependence of light intensity of Voc for FASnI 3, FASnI 3 - BAI 15 % and FASnI 3 -EDAI 1% devices. 15

16 # (a) FASnI3 (b) FASnI3-15% BAI (c) * FASnI3-1% EDAI * Intensity /a.u. # * * after 6hr after 3hr Intensity /a.u. after 6hr after 3hr Intensity /a.u. * * after 6hr after 3hr (0) fresh fresh fresh /degree /degree /degree gure S13. X-ray diffraction patterns of films of (a) FASnI 3, (b) FASnI 3 -BAI 15 %, (c) FASnI 3 - EDAI 1 % exposed to ambient conditions (50 % humidity and 0 C) from 0 to 6 h. Symbols * represents the contribution of the ITO substrate and # related to SnI 4. Fi

17 (a) Current Density /ma cm Condition J SC /ma cm - V OC /V FF PCE /% Fresh After 7 days After 13 days After 8 days After 41 days Voltage /V fresh 7 days 13 days 8 days 41 days (b) 0 Current Density /ma cm Condition J SC /ma cm - V OC /V FF PCE /% Fresh After days After 4 days After 30 days After 37 days Voltage/V fresh days 4 days 30 days 37 days Current Density /ma cm - (c) Condition J SC/ /ma cm - Fresh After 7 days After 13 days After 0 days After 38 days V OC /V FF PCE /% Voltage /V fresh 7 days 13 days 0 days 38 days (d) Current Density /ma cm Condition J SC /ma cm - V OC /V FF PCE /% Fresh After 7 days After 30 days After 40 days After 60 days Voltage /V fresh 7 days 30 days 40 days 60 days Figure S14. Current-voltage curves of four FASnI 3 -EDAI 1 % devices at varied durations of storage showing a similar trend of the effect of slow passivation as in Figure 4a of the main text 17

18 Voc /V Fresh 5-days 11-0days 1-30days more than 30 days Jsc /ma cm Fresh 5-days 11-0days 1-30days more than 30 days Fresh 5-days 11-0days 1-30days more than 30 days Figure S15. Statistical boxplots showing the variations of Voc, Jsc and FF for 0 encapsulated FASnI 3 -EDAI 1 % devices for varied durations of storage FF

19 Intensity /a.u. Raw Intensity Peak Sum Background Sn + Sn 4+ Sn + /% Sn 4+ /% Binding energy /ev Figure S. X-ray photoelectron spectra showing the Sn + /Sn 4+ proportions on the surface of a FASnI 3 -EDAI 1 % film after 7 days 19

20 (a) (b) Figure S17. SEM images of samples of (a) FASnI 3-5%BAI-1%EDAI and (b) FASnI 3-15%BAI- 1%EDAI films. 0

21 Intensity /a.u. 15% BAI+1% EDAI 5% BAI+%1 EDAI 15% BAI /degree Figure S. XRD pattern of samples of FASnI 3 -xbai-yedai films with varied proportions x and y. 1

22 Intensity /a.u. FASnI 3 -BAI 5%-EDAI 1%-After 9 Days FASnI 3 -BAI 5%-EDAI 1%-After 5 Days FASnI 3 -BAI 5%-EDAI 1%-Fresh /Degree Normalized PL Intensity FASnI 3 -BAI 5%-EDAI 1%- Fresh FASnI 3 -BAI 5%-EDAI 1%- After 5 Days FASnI 3 -BAI 5%-EDAI 1%- After 9 Days Time /ns Figure S19. XRD and TCSPC results of fresh and aged (storage periods 5 and 9 days) thin-film sample FASnI 3 -BAI 5%-EDAI 1%.

23 0 Current Density /ma cm FASnI 3 5% BAI +0.8% EDAI 5% BAI+1% EDAI % BAI+1% EDAI 15% BAI+1% EDAI 5% BAI+% EDAI 15% BAI+% EDAI Voltage /V Figur e S0. Current-voltage curves of devices with FASnI 3 -xbai-yedai perovskites at varied proportions x and y 3

24 Table S1. Proportion of Sn + and Sn 4+ in various samples at two positions; surface and bulk (after etching 30 s) Samples Sn + /% Sn 4+ /% Sn + /% Sn 4+ /% Without etching (surface) After etching for 30 s (bulk) FASnI FASnI 3 -BAI 15 % FASnI 3 -EDAI 1 % Table S. Time coefficients (relative amplitudes) of the corresponding perovskite films derived from fitting of PL transients (Figure e) Samples τ 1 /ns (A 1 ) τ /ns (A ) τ ave /ns FASnI 3 0. (1.0) FASnI 3 -BAI 15% 0.4 (1.0) FASnI 3 -EDIA 1% 0.6 (0.34) 1.57 (0.66)

25 Table S3. Photovoltaic parameters of inverted planar heterojunction perovskite solar cells fabricated with varied proportion x in FASnI 3 -xbai under simulated AM-1.5G illumination (power density 0 mw cm ) Devices J SC /ma cm - V OC /V FF PCE /% FASnI 3 best average 17.± ± ± ± 0. BAI % best average 14.3± ± ± ±0.3 BAI 15 % best average 17.± ± ±0.0 5.±0. BAI 0 % best average 15.6± ± ± ±0.4 BAI 5 % best average 13.6± ± ± ±0.3 5

26 Table S4. Photovoltaic parameters of inverted planar heterojunction perovskite solar cells fabricated with varied proportion y in FASnI 3 -yedai under simulated AM-1.5G illumination (power density 0 mw cm ) Devices Jsc /ma cm - Voc /V FF PCE /% FASnI 3 best average 17.± ± ± ± 0. EDAI 1 % best average.9± ± ± ±0.5 EDAI % best average 13.9± ± ± ±0.4 EDAI 3 % best average.5± ± ± ±0.3 6

27 Table S5. Photovoltaic parameters of inverted planar heterojunction perovskite solar cells fabricated with FASnI 3 under simulated AM-1.5G illumination (power density 0 mw cm ) with active area 0.05 cm Cell no. Voc /V Jsc /ma cm - FF PCE /%

28 Table S6. Photovoltaic parameters of inverted planar heterojunction perovskite solar cells fabricated with FASnI 3 -BAI 15 % under simulated AM-1.5G illumination (power density 0 mw cm ) with active area 0.05 cm Cell No. Voc /V Jsc /ma cm - FF PCE /%

29 Table S7. Photovoltaic parameters of inverted planar heterojunction perovskite solar cells fabricated with FASnI 3 -EDAI 1 % under simulated AM-1.5G illumination (power density 0 mw cm ) with active area 0.05 cm Cell No. Voc /V Jsc /ma cm - FF PCE /%

30 Table S8. Coefficients (relative amplitudes) of the FASnI 3 -EDAI 1% films in tracking the time experiment obtained from fitting the PL transients (Figure 4) Samples τ 1 /ns (A 1 ) τ /ns (A ) τ ave /ns Fresh 0.6 (0.34) 1.57 (0.66) 1.47 After 5 days 1. (0.40).03 (0.60) 1.78 After 15 days 1.45 (0.86) 3.64 (0.14).11 After 0 days.57 (0.65) 5.80 (0.35) 4.34 After 33 days 4.71 (0.83) 15.1 (0.17)

31 Table S9. Photovoltaic parameters of inverted planar heterojunction perovskite solar cells fabricated with varied proportions x and y in FASnI 3- xbai-yedai under simulated AM-1.5G illumination (power density 0 mw cm ). Devices J SC /ma cm - V OC /V FF PCE /% FASnI BAI 5 %-EDAI 0.8 % BAI 5 %-EDAI 1 % BAI %-EDAI 1 % BAI 15 %-EDAI 1 % BAI 5 %-EDAI % BAI 15 %-EDAI %