High thermoelectric performance based on CsSnI3 thin films with improved stability†
Tin-based metal halide perovskites have been considered as promising candidates in the field of thermoelectric materials due to their ultralow thermal conductivity and considerable electrical conductivity. However, the mechanism of air exposure to self-dope the films for enhanced thermoelectric properties raises questions about their stability for thermoelectric applications. Here, we report increased air stability of sequential thermally evaporated CsSnI3 thin films without using any additives. This was achieved by adjustment of the order of deposition of the precursor materials. The optimised films show more than an order of magnitude less degradation in electrical conductivity in air over 60 minutes than control samples and have optical signatures of degradation in air that take ∼5 times longer to emerge. Conversely, we show that the rate of self-doping through oxidation of Sn2+ to Sn4+ is substantially enhanced at elevated temperatures and characterise its impact on thermal and electrical transport properties. Furthermore, we obtain a figure of merit (zT) of 0.08 for CsSnI3 thin films in this more stable configuration.