Supporting Information for Two-dimensional homologous perovskites as light absorbing materials for solar cell applications Duyen H. Cao, Constantinos C. Stoumpos, Omar K. Farha,, Joseph T. Hupp, and Mercouri G. Kanatzidis*, Department of Chemistry and Argonne-Northwestern Solar Energy Research (ANSER) Center, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States Department of Chemistry, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia Table of contents Section S1. Experimental Section S2. Images of bulk 2D perovskite materials Section S3. X-ray diffraction patterns Section S4. SEM-EDS elemental analysis of perovskite thin films Section S5. Top surface and cross-sectional SEM images of perovskite thin films Section S6. Work function Section S7. Additional photo-voltage responses of (C 4 H 9 NH 3 ) 2 (CH 3 NH 3 ) 2 Pb 3 I 10 -based devices S1
Section S1. Experimental Material characterization. Powder and film X-ray diffraction patterns were collected using a CPS 120 INEL X-ray diffractometer (Cu Kα, 1.5406 Å) operating at 40 kv and 20 ma. Optical diffuse-reflectance spectra were collected at room temperature using a Shimadzu UV-3600 PC double-beam, double-monochromator spectrophotometer operating from 200 to 2500 nm. BaSO 4 was used as a non-absorbing reflectance reference. Photoluminescence spectra were collected using a fluorometer in which the light source was a xenon lamp. The excitation wavelengths were 640 nm, 620 nm, 550 nm, 500 nm, and 400 nm for CH 3 NH 3 PbI 3, (n-c 4 H 9 NH 3 ) 2 (CH 3 NH 3 ) n- 1Pb n I 3n+1 (n = 4, 3, 2, 1), respectively. Work function was probed using ultraviolet photoelectron spectroscopy (UPS) under high vacuum with He I gas as an ultraviolet light source (21.20 ev). Scanning electron microscope (SEM) images were acquired at an accelerating voltage of 5 to 20 kv using a Hitachi SU8030 instrument equipped with an Oxford X-max 80 SDD EDS detector. Device characterization. Photovoltaic responses (J V curves) were measured under AM1.5G sunlight irradiance (100 mw cm -2 ) generated by a xenon arc lamp of a Spectra-Nova Class A solar simulator, with the intensity calibrated by using an NREL-certified mono-crystalline Si diode coupled to a KG3 filter to get a spectral mismatch to unity. A Keithley 2400 series source meter was used to collect J-V data. The active area of all devices was 17.5 mm 2, but limited to a 14 mm 2 aperture via a mask during the measurement. Section S2. Images of bulk materials Figure S1. a) Images of as synthesized 2D (C 4 H 9 NH 3 ) 2 (CH 3 NH 3 ) n-1 Pb n I 3n+1 (n = 1, 2, 3, 4, ) bulk materials, b) SEM image of (C 4 H 9 NH 3 ) 2 (CH 3 NH 3 ) 3 Pb 3 I 10 single crystals S2
Section S3. X-ray diffraction patterns Figure S2. X-ray diffraction patterns of a) single crystal, b) powder, and c) thin films of (C 4 H 9 NH 3 ) 2 (CH 3 NH 3 ) n-1 Pb n I 3n+1 (n = 1, 2, 3, 4, ) materials. Note that the number of perovskite slabs (n = 1, 2, 3, 4, ) is well reflected by the number of reflections below 2 theta of 12 degree. S3
Section S4. SEM-EDS elemental analysis of perovskite thin films 1. CH 3 NH 3 PbI 3 2. (C 4 H 9 NH 3 ) 2 (CH 3 NH 3 ) 3 Pb 4 I 13 3. (C 4 H 9 NH 3 ) 2 (CH 3 NH 3 ) 2 Pb 3 I 10 4. (C 4 H 9 NH 3 ) 2 (CH 3 NH 3 )Pb 2 I 7 5. (C 4 H 9 NH 3 ) 2 PbI 4 S4
Summary of SEM-EDS results Table S1. SEM-EDS elemental analysis of (C 4 H 9 NH 3 ) 2 (CH 3 NH 3 ) n-1 Pb n I 3n+1 (n = 1, 2, 3, 4, ) perovskite thin films Compound Pb I Experimental Theoretical Error (%) (Atomic %) (Atomic %) I : Pb ratio I : Pb ratio MAPbI 3 3.33 9.77 2.93 3.00 2.20 (BA) 2 (MA) 3 Pb 4 I 13 2.62 8.46 3.23 3.25 0.65 (BA) 2 (MA) 2 Pb 3 I 10 2.36 7.61 3.22 3.33 3.17 (BA) 2 (MA)Pb 2 I 7 2.27 8.34 3.67 3.50 4.97 (BA) 2 PbI 4 1.28 5.26 4.11 4.00 2.73 *Note: for the purpose of only comparing I : Pb ratio, we do not include atomic % of other elements such as Ti, O, C, N. S5
Section S5. Top surface and cross-sectional SEM images Figure S3. Top surface SEM images of 3D, intermediate 2D and 2D perovskite thin films Figure S4. Cross sectional SEM image of a functional (BA) 2 (MA) 2 Pb 3 I 10 device S6
Section S6. Work function Figure S5. (He I) UPS spectra of (BA) 2 (MA) n-1 Pb n I 3n+1 (n = 1, 2, 3, 4, ) compounds S7
Section S7. Additional photo-voltage responses of (BA) 2 (MA) 2 Pb 3 I 10 -based devices Figure S6. J-V curves of (BA) 2 (MA) 2 Pb 3 I 10 -based devices using different TiO 2 thicknesses and different perovskite precursor concentrations Figure S7. Comparative plots of J sc (green) and V oc (purple) of (BA) 2 (MA) 2 Pb 3 I 10 -based devices as a function of TiO 2 thickness using 1.8 M perovskite precursor solutions S8
Figure S8. Average photo-voltage performance of (BA) 2 (MA) 2 Pb 3 I 10 -based devices using 350 nm thick TiO 2 layer and 1.8 M Pb 3 I 10 precursor concentration Figure S9. J-V curves of fresh and after 2 months exposing to humidity of (BA) 2 (MA) 2 Pb 3 I 10 - based devices S9