Photoelectronic properties of lead-free CH3NH3SnI3 perovskite solar cell materials and devices

Intensive research on lead halide perovskites clarified that these materials are indeed suitable candidates for photovoltaic applications due to their excellent photoelectronic properties. Yet, lead is considered a major issue for commercialization. Concurrently, in the last five years, increasing research efforts have been made to replace lead with tin. Although partially successful, the present conversion efficiencies of tin halide perovskite solar cells are limited. Further performance improvements should be possible, if the underlying energy loss mechanisms in these devices can be clarified. Here, we investigated the energy loss mechanisms in lead-free CH₃NH₃SnI₃ (MASnI₃) solar cells as well as intrinsic photoelectronic properties of MASnI₃ to assess its potential for photovoltaics. Time-resolved photoluminescence (PL) measurements reveal that the short-circuit current (Jsc) in the MASnI₃ solar cell deviates from an ideal value as a result of fast recombination of photogenerated carriers in the perovskite layer. Consequently, a larger Jsc should be possible with longer carrier lifetimes. Furthermore, resonantly excited PL and temperature-dependent PL data clearly reveal that the intrinsic electron–longitudinal optical phonon coupling governs the broadening of optical transitions at around 300 K. By performing a detailed comparison of the data of MASnI₃ and MAPbI₃, it is shown that the intrinsic optical properties of tin and lead perovskites are similar to each other. Our results suggest that solar cells based on tin halide perovskites can compete with lead halide perovskite solar cells, if the carrier lifetimes can be improved.