Simultaneous Enhancement of Thermoelectric Power Factor and Phase Stability of Tin-Based Perovskites by Organic Cation Doping

Tin-based halide perovskites are promising room-temperature thermoelectric materials due to their ultralow thermal conductivity and propensity for doping. However, poor phase stability and inferior electrical transport properties hinder their practical application. Herein, we found that organic cation formamidinium (FA) doping, which is not possible by high-temperature processing, could simultaneously enhance the stability and electrical conductivity of CsSnI3 films through a simple solution process. The carrier concentration of 3 × 1019 cm–3 was obtained in FA-doped films, which leads to an 8× enhancement in electrical conductivity to 26.5 S cm–1 but maintains a Seebeck coefficient as high as 131 μV K–1, resulting in a power factor of 45.53 μW m–1 K–2. A further theoretical calculation shows that the enhanced carrier concentration originates from the lowered transition energy of tin vacancies in the doped films. More importantly, remarkable phase stability is achieved under an ambient atmosphere, which stems from a sharply decreased free energy of the B-γ phase compared to the Y phase by FA doping. This work suggests that organic cation doping by facile solution processing is an avenue for the simultaneous improvement of the thermoelectric power factor and phase stability of tin-based halide perovskite. It is applicable for flexible and wearable thermoelectric generators to harvest energy from low-grade heat sources.