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Formation of Stable Tin Perovskites Co-crystallized with Three Halides for Carbon-based Mesoscopic Lead-free Perovskite Solar Cells
C.-M. Tsai, N. Mohanta, C.-Y. Wang, Y.-P. Lin, Y.-W. Yang, C.-L. Wang, C.-H. Hung, and E. W.-G. Diau*


We synthesized and characterized methylammonium (MA) mixed tri-halide tin perovskites (MASnIBr2−xClx) for carbon-based mesoscopic solar cells free of lead and hole-transporting layers. Varied SnCl2/SnBr2 ratios yielded tin perovskites with three halides (I, Br, and Cl) co-crystallized inside the tin-perovskite. When the SnCl2 proportion was ≥50 % (x≥1), phase separation occurred to give MASnI3−yBry and MASnCl3−zBrz in the stoichiometric proportions of their precursors, confirmed by XRD. A device with MASnIBr1.8Cl0.2 (SnCl2=10 %) showed the best photovoltaic performance: JSC=14.0 mA cm−2, VOC=380 mV, FF=0.573, and PCE=3.1 %, and long-term stability. Electrochemical impedance spectra (EIS) show superior charge recombination and dielectric relaxation properties for the MASnIBr1.8Cl0.2 cell. Transient PL decays showed the intrinsic problem of tin-based perovskites with average lifetimes less than 100 ps.

Angew. Chem. Int. Edit. 56, 13819 (2017)