Photophysics of tin-lead halide perovskites for tandem photovoltaics Yueyao Dong 2 and Wen-Xian Zhu 1 , Chieh-Ting Lin 2 , Thomas J Macdonald 1 1 School of Engineering and Materials Science, Queen Mary University of London, Mile End Road, London E1 4NS, UK, 2 Department of Chemical Engineering, National Chung Hsing University, No.145, Xingda Road, South District, Taichung 40227. e-mail: yueyao.dong@qmul.ac.uk;g111065005@mail.nchu.edu.tw;c.lin15@nchu.edu. tw;t.j.macdonald@qmul.ac.uk Due to the outstanding optoelectronic properties and wide applications of organic-inorganic metal halide perovskites, they have attracted enormous attention throughout the photovoltaic community. Perovskite solar cells (PSCs) using lead (Pb) halide perovskites can now reach over 25% power conversion efficiency (PCE), retaining over 90% of their original PCE after 500 hours of light exposure. [1] However, the energy bandgaps of Pb halide perovskites are larger than the ideal bandgap for single junction solar cells, according to the Schokley-Queisser (SQ) radiative limit. Mixed tin-lead (Sn-Pb) halide perovskites will play a pivotal role in approaching the SQ limit where their bandgap can be tuned to below 1.2 eV, which is promising to fabricate highly efficient all-perovskite tandem solar cells. In this work, we report the photophysics behind using guanidium thiocyanate (GASCN) as an additive to improve the mixed Sn-Pb halide perovskite thin film quality and the resulting device performance. We discuss trends in steady-state and time-resolved photoluminescence spectroscopy and compare the quantum yields of the polycrystalline films. This provides new design rules to understand GASCN additives in low-bandgap Sn-Pb halide perovskite thin films and devices, promoting further research into various approaches to obtain efficient tandem solar cells. References 1. Min, H., Lee, D.Y., Kim, J.et al.Perovskite solar cells with atomically coherent interlayers on SnO2electrodes.Nature598, 444–450 (2021). 2. Kim, H.,Lee, J. W.,Han, G. R.,Kim, Y. J.,Kim, S. H.,Kim, S. K.,Kwak, S. K.,Oh, J. H.,Highly Efficient Hole Transport Layer- Free Low Bandgap Mixed Pb–Sn Perovskite Solar Cells Enabled by a Binary Additive System. Adv. Funct. Mater. 2022,32, 2110069. 3. Feng Lv, Yanqing Yao, Cunyun Xu, Dingyu Liu, Liping Liao, Gang Wang, Guangdong Zhou, Xusheng Zhao, Debei Liu, Xiude Yang, and Qunliang Song. ACS Applied Energy Materials 2021 4 (2), 1294-1301
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