Synthesis and Structural Characterization of SnO2 Electron Transport Layer in Perovskite Solar Cells Synthesis and Structural Characterization of SnO2 Electron Transport Layer in Perovskite Solar Cells Hongzhou Dong1, Chenglin Gao1, Xichang Bao2, Liyan Yu1, Lifeng Dong1,3 1. College of Materials Science and Engineering, Qingdao University of Science and Technology, Qingdao 266042, China 2. CAS Key Laboratory of Bio-based Materials, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao 266101, China 3. Department of Physics, Hamline University, St. Paul, MN 55104, USA Energy crisis and environmental pollution become the problems that more and more researchers focus on, and perovskite solar cells have attracted most interesting due to their high-power conversion efficiency (PCE) of over 20% [1]. TiO2 is usually utilized as electron transporting layer for perovskite solar cells, but its high synthesis temperature of 450 °C has limited its applications in flexible electronics. In comparison to TiO2, SnO2 can be synthesized through low temperature solution process and exhibit similar or even better electrical and optical properties. In this study, we synthesize SnO2 by spin-coating followed by thermal treatment at 200 °C and study its structural and photoelectrical properties. Figures 1a-b demonstrate schematic structure and energy band diagram of a perovskite solar cell, respectively. For the fabrication of a solar cell, fluorine doped tin oxide (FTO) glass substrate was firstly cleaned and treated with O2 plasma to improve wettability. SnO2 was then synthesized on the surface of the FTO substrate by spin-coating SnCl4·5H2O precursor at 4000 rpm for 20 s, followed by thermal treatment at 200 °C for 30 min. Then, perovskite CH3NH3PbI3 and thiophene copolymer P1 as hole transporting layer [2] were formed on top of SnO2 layer by spin-coating successively. At the end, the sample was taken into a thermal evaporation chamber, where Ag electrode was deposited. Surface morphology of the films was characterized by scanning electron microscopy (SEM, Hitachi S-4800). Current-voltage (J-V) curves of solar cells were tested under 100 mW/cm2 illumination of AM 1.5G with a Newport solar simulator through a Keithley 2420 source measurement unit [3]. As shown in Figure 2a, a compact SnO2 nanocrystalline film is formed on the FTO substrate with a thickness of circa 30 nm (Figure 2c). Figure 2b shows high quality perovskite CH3NH3PbI3 film with relatively large grains and excellent surface coverage is coated on the top of the SnO2 layer. As given in Figure 2d, short-circuit current density (JSC), open-circuit voltage (VOC), fill factor (FF) and PCE of the perovskite solar cells are 9.22 mA/cm2, 1.05 V, 65.01%, and 6.27%, respectively. This indicates that SnO2 film can be successfully synthesized by low temperature solution process to replace TiO2 or organic PEDOT/PSS as electron transporting layer for perovskite solar cells, and the PCE can be improved by optimizing parameters of solution process [4]. References: [1] Qianqian Zhu et al, ACS Appl. Mater. Interfaces 8 (2016), p. 2652. 2222 doi:10.1017/S143192761901184X Microsc. Microanal. 25 (Suppl 2), 2019 © Microscopy Society of America 2019 https://doi.org/10.1017/S143192761901184X Downloaded from https://www.cambridge.org/core. Carnegie Mellon University, on 06 Apr 2021 at 01:14:28, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S143192761901184X https://www.cambridge.org/core https://www.cambridge.org/core/terms [2] Hugo Bronstein et al, J. Am. Chem. Soc. 133 (2011), p. 3272. [3] Chenglin Gao et al, J. Mater. Chem. C 6 (2018), p. 8234. [4] This research was supported by the National Natural Science Foundation of China (21776147 & 21606140), the International Science & Technology Cooperation Program of China (2014DFA60150), the Department of Science and Technology of Shandong Province (2016GGX104010), and Shandong Province Higher Educational Science and Technology Program (J16LA14). Figure 1. Schematic structure of a perovskite solar cell (a) and corresponding energy band diagram (b). Figure 2. Top-view SEM images of SnO2 film coated on FTO substrate (a) and perovskite CH3NH3PbI3 film coated on the SnO2 film (b). Cross sectional SEM image (c) and J-V curve (d) of the perovskite solar cell. Microsc. Microanal. 25 (Suppl 2), 2019 2223 https://doi.org/10.1017/S143192761901184X Downloaded from https://www.cambridge.org/core. Carnegie Mellon University, on 06 Apr 2021 at 01:14:28, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S143192761901184X https://www.cambridge.org/core https://www.cambridge.org/core/terms