Relationship between Relative Lattice Strain and Efficiency for Sn-Perovskite Solar Cells
Kohei Nishimura a, Daisuke Hirotani a, Gaurav Kapil b, Chi Huey Ng a, Kengo Hamada a, Kamarudin, Muhammad Akmal a, Ripolles Teresa c, Shen Qing d, Satoshi likubo a, Takashi Minemoto e, Kenji Yoshino f, Hiroshi Segawa b, Shuzi Hayase a
a Kyushu Institute of Technology, 204 Hibikino Wakamatsu-ku, Kitakyushu - Fukuoka, 808, Japan
b The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, Japan
c Universidad Rey Juan Carlos, C/Tulipan s/n, Móstoles, 28933
d University of Electro-Communication
e Ritsumeikan University, 1-1-1 norohigashi Kusatsu, Japan
f Miyazaki University, 1-1 Gakuen, Kibanadai-nishi, Miyazaki 889-2192, Japan
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV19)
Roma, Italy, 2019 May 12th - 15th
Organizers: Prashant Kamat, Filippo De Angelis and Aldo Di Carlo
Invited Speaker Session, Shuzi Hayase, presentation 041
Publication date: 11th February 2019

Sn-perovskite solar cells are known as narrow band-gap solar cells which is expected to give higher efficiency than Pb perovskite solar cells from the view point of the narrow band gap energy, and is to be useful for the bottom layer for all-perovskite-tandem solar cells. We have already reported 20.4% efficiency for SnPb perovskite solar cells (1-3) and SnGe perovskite solar cells with 7.9% efficiency (4,5). There are some items which limit the enhancement of the efficiency. In this report, one of which, relationship between lattice strain and the efficiency is discussed. In the composition of QFAMASnI3, Q was changed with Na+, K+, Cs+, Ethylammonium+(EA) and Butylammonium+ (BA) respectively, and the relationship between the lattice strain obtained from XRD and the photovoltaic performances were discussed. The efficiency of the solar cells with the Sn-perovskite solar cell had linear relationship with the relative lattice strain. Among them, EAFAMASnI3 having least lattice strain gave the results of 7.6 %. The second item is trap distribution. The distribution of trap states within perovskite vicinity or hetero-interfaces is attributed to the low photovoltaic performances. Thermally stimulated current (TSC) was used for the evaluation of the trap states. The addition of 5 mole% germanium into the FAMASnI3 (FMSGI) suppressed the trap density from 1015-1017 cm-3 (without Ge) to 108-1014 cm-3 and gave longer charge diffusion length (~1 μm) to give 7.9% efficiency. In addition, on the SnPb perovskite solar cells, the relationship between the lattice strain and efficiency was discussed. By decreasing the lattice strain, the efficiency was enhanced to > 20%.

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