Tunable Band Gap and Long Carrier Recombination Lifetime of Stable Mixed CH₃NH₃Pb_xSn_{1- x}Br₃ Single Crystals

The mixed metal Pb/Sn halide perovskites have drawn significant attentions in perovskite photovoltaics due to their broad absorption spectra and tunable band gaps. To obtain a deeper understanding of these materials properties, single crystals are regarded as the best platform among various building blocks for fundamental study. Here, we report the mixed-metal MAPb_xSn_1-xBr₃ (MA = CH₃NH₃) perovskite single crystals grown by top seeded solution growth (TSSG) method. Systematical characterizations were applied to investigating their structures and optoelectronic properties. These single crystals kept higher stability even exposed to air over one month than that of MASnBr₃. The outstanding electrical properties, such as lower trap-state density and higher carrier mobility, were investigated by space charge-limited current (SCLC) and the Hall Effect measurements. More importantly, these perovskite single crystals exhibited much narrower optical band gap (1.77 eV) and longer carrier lifetime (∼2 μs) than those of MAPbBr₃ and MASnBr₃, which showed a greatly potential application in tandem solar cells based on hybrid organic-inorganic perovskites with the optimal bandgap of 1.70-1.85 eV.