Enhanced Thermoelectric Performance in Lead-Free Inorganic CsSn_1–xGe_xI₃ Perovskite Semiconductors

Halide perovskite semiconductors exhibit ultralow thermal conductivities, making them potentially suitable for thermoelectric applications. Nevertheless, the thermoelectric properties of the prototypical halide perovskite of CH3NH3PbI3 have been limited with a very low dimensionless figure of merit (ZT) and a narrow operating temperature window, which are attributed to its poor electronic conductivity and unstable hybrid organic–inorganic composition, respectively. Here, we report the bulk synthesis of a stable, all-inorganic halide perovskite of CsSn0.8Ge0.2I3 as a new thermoelectric material, which shows a 10 order of magnitude enhancement in ZT compared with that of CH3NH3PbI3 and an operating temperature as high as 473 K. Importantly, this CsSn0.8Ge0.2I3 perovskite is also Pb-free in the composition, attesting its high potential as an environmentally friendly candidate material for future thermoelectrics.