Ultrahigh thermoelectric performance in RbGeI3/CsSnI3 superlattices

By first-principles methods combined with Boltzmann transport theory, we perform a systematic investigation of the thermoelectric properties of RbGeI₃/CsSnI₃ superlattices. RbGeI₃/CsSnI₃ superlattices construct a quantum well with valence and conduction states near the Fermi level located in CsSnI₃ layers, which yields a periodic repetition of two-dimensional transport channels. The quantum-confinement effects and the ultralow lattice thermal conductivity of the superlattices greatly enhance the in-plane thermoelectric power factor and figure of merit (ZT), which further increase when decreasing the thickness of CsSnI₃ layers in the superlattices. In (RbGeI₃)₅/(CsSnI₃)₁ superlattice, the power factor increases by two times, and ZT is enhanced by nine times, compared to the parent CsSnI₃. The ZT of this superlattice is 1.34 at 300 K and 3.78 at 550 K, providing a potential candidate for room-temperature thermoelectric applications. These results also confirm a way to improve the thermoelectric performance of CsSnI₃.