Supporting Information

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1 Supporting Information Facile synthesis and characterization of sulfur doped low band gap bismuth based perovskites by soluble precursor route Murugan Vigneshwaran a *, Takeshi Ohta a, Satoshi Iikubo a, Gaurav Kapil a, Teresa Ripolles a, Yuhei Ogomi a, Tingli Ma a, Shyam S. Pandey a, Shen Qing b, Taro Toyoda b, Kenji Yoshino c, Takashi Minemoto d, Shuzi Hayase a * a Graduate School of Life Science and Systems Engineering, Department of Biological Functions and System, Kyushu Institute of Technology, 2-4 Hibikino, Wakamatsu-ku, Kitakyushu , Japan. Fax: ; Tel: b Department of Engineering Science, Faculty of Informatics and Engineering, The University of Electro-Communications, Chofugaoka, Chofu, Tokyo , Japan. c Department of Electrical and Electronic Engineering, Miyazaki University, 1-1 Gakuen Kibanadai-nishi, Miyazaki , Japan. d Department of Photonics, Faculty of Science and Engineering, Ritsumeikan University, Noji Higashi, Kusatsu, Siga , Japan.

2 Materials and methods Synthesis of bismuth (III) ethyl xanthate Bismuth (III) nitrate pentahydrate (30.9 g, 63.7 mmol) was dissolved in 500 ml of deionized water and 55 ml of hydrochloric acid was added until suspension became clear. A solution of potassium ethyl dithiocarbonate (32.7 g, mmol) in 100 ml of deionized water was added under stirring and a yellow solid was formed immediately. After the reaction solution was stirred for 1 hour, the yellow precipitate was filtered and dried under vacuum. The residue was added in deionized water and dispersed by ultrasonic treatment. After the soluble side products were removed by filtration, the residue was washed thoroughly with deionized water and dried under vacuum. Undoped and Sulfur doped MBI samples fabrication For the preparation of sulfur doped MBI, glass substrates were cleaned in the order by distilled water, acetone, and isopropanol for each 15 minutes. Mesoscopic TiO 2 layer was spin coated on the glass substrate by diluting PST-30NRD paste (Dyesol) with ethanol in the ratio of 1: 3 at 5000rpm for 30 seconds. After that prepared films were annealed at 500 ᵒC for 30 minutes. The precursor solution was prepared by mixing Bi(xt) 3 and MAI in the molar ratio of 1:2. DMF was used as the solvent and after stirring it continuously for 10 minutes the solution was filtered using 0.45 µm PTFE filter. MBI films was formed by spin coating the precursor solution at 2000 rpm for 15 sec. After spin coating the films was post annealed at different temperatures like 80ᵒC, 120ᵒC, and 150ᵒC. Undoped MBI samples were prepared according to the demonstration of Park et al.[4] Crystallographic and morphology studies XRD patterns for sulfur doped MBI were studied using X-ray diffractometer RINT- Ultima III, Rigaku, Japan employing Cu Ka1 radiation (k = Å). Diffracted rays were registered for every 0.02 of Bragg angle from 10 to 60. Before the measurement of sample standard silicon samples was measured for calibrating and X-ray intensity for TiO 2 /glass was also checked. Surface morphology of the samples was studied through FE-SEM (Hitachi, S- 5200). Optical absorption and FTIR studies Jasco V-550 UV vis spectrophotometer were used for recording the absorption spectra for sulfur doped MBI. Glass coated with mesoporous TiO 2 was used as the reference for the correction of background. Jasco FTIR 4100 was used for the measuring the FTIR spectra for the samples in transmission mode. XPS studies

3 Wide and high resolution XPS measurements for sulfur doped MBI was performed using Shimadzu/Kratos Axis HSi. AlKα radiation were employed for measuring the samples at the pressure of mbar. Specific core level were repetitively measured in order to minimize the charging and radiation effects. TG-DTA and Photoelectron yield spectroscopy studies (PYS) studies Thermogravimetric/Differential Thermal Analyzer (TG-DTA) measurements were performed using Shimadzu DTG-60 model. Four milligram of Bi(xt) 3 powder was heated at the rate of 20 ᵒC/min from ambient temperature to 500 ᵒC with nitrogen as purge gas. PYS spectra for the samples were analyzed using PYS, Bunkoukeiki Co., Ltd., BIP-KV201. In preparing samples, sulfur doped MBI was coated over the FTO substrate and post heated at different temperatures. Figure S1. Comparison of sulfur doped MBI XRD Patterns with precursor materials and bismuth sulfide (a) Bi(xt) 3 + 2MAI at 150 ᵒC (b) Bismuth sulfide powder (c) Methyl ammonium iodide powder (d) Bismuth ethyl xanthate powder.

4 Figure S2. Tauc plots for undoped and sulfur doped MBI at various post heating temperatures.

5 Figure S3. FTIR spectrum of Bi(xt) 3 powder and sulfur doped MBI at different temperatures. Figure S4. TG-DTA for Bi(xt) 3 powder. Figure S5. XPS spectra of sulfur doped MBI at different temperatures in wide range.

6 Figure S6. Photoelectron yield spectroscopy of sulfur doped MBI post annealed at different temperature. Figure S7. Energy band diagram for undoped MBI and sulfur doped MBI post heated at different temperatures

7 Figure S8. FE-SEM images of sulfur doped MBI post annealed at different temperature (a and a1) 80 ᵒC, (b and b-1) 120 ᵒC, (c and c-1) 150 ᵒC. Material Carrier concentration Table S1. Comparison of Hall-Effect measurement Mobility

8 Sulfur doped MBI at 120 ᵒC cm cm 2.v -1 s -1 Undoped MBI cm-3[1] 1 cm 2.v -1 s -1 [1] Lead perovskites (MAPbI 3 ) cm -3 [2] 8.2 cm 2.v -1 s -1 [3] REFERENCES (1) Lyu, M.; Yun, J.-H.; Cai, M.; Jiao, Y.; Bernhardt, P. V; Zhang, M.; Wang, Q.; Du, A.; Wang, H.; Liu, G.; Wang, L. Organic-Inorganic Bismuth (III)-Based Material: A Lead- Free, Air-Stable and Solution-Processable Light-Absorber beyond Organolead Perovskites. Nano Res. 2016, 9 (3), (2) Bi, C.; Shao, Y.; Yuan, Y.; Xiao, Z.; Wang, C.; Gao, Y.; Huang, J. Understanding the Formation and Evolution of Interdiffusion Grown Organolead Halide Perovskite Thin Films by Thermal Annealing. J. Mater. Chem. A 2014, 2 (43), (3) Wehrenfennig, C.; Eperon, G. E.; Johnston, M. B.; Snaith, H. J.; Herz, L. M. High Charge Carrier Mobilities and Lifetimes in Organolead Trihalide Perovskites. Adv. Mater. 2014, 26 (10), (4) Park, B.-W.; Philippe, B.; Zhang, X.; Rensmo, H.; Boschloo, G.; Johansson, E. M. J. Bismuth Based Hybrid Perovskites A3Bi2I9 (A: Methylammonium or Cesium) for Solar Cell Application. Adv. Mater. 2015, 27 (43),