First-principles predictions of enhanced thermoelectric properties for Cs₂SnI₂Cl₂ and Cs₂PbI₂Cl₂ monolayers with spin–orbit coupling

Inspired by the exceptional charge transport properties and ultra-low thermal conductivity of halide perovskite, we investigate the electronic nature, thermal transport, and thermoelectric properties for Ruddlesden-Popper all-inorganic perovskite, Cs2SnI2Cl2and Cs2PbI2Cl2monolayers, using first-principles calculations. During the calculations, spin-orbit coupling has been considered for electronic transport as well as thermoelectric properties. The results show that the Cs2SnI2Cl2and Cs2PbI2Cl2monolayers exhibit high carrier mobility and low thermal conductivity. Stronger phonon-phonon interaction is responsible for the fact that thermal conductivity of Cs2SnI2Cl2monolayer is much lower than that of Cs2PbI2Cl2monolayer. At 700 K, the values of the figure of merit (ZT) for the n-type doped Cs2SnI2Cl2and Cs2PbI2Cl2monolayers are about 1.05 and 0.32 at the optimized carrier concentrations 5.42 × 1012cm-2and 9.84 × 1012cm-2. Moreover, when spin-orbit coupling is considered, the correspondingZTvalues are enhanced to 2.73 and 1.98 at 5.27 × 1011cm-2and 6.16 × 1011cm-2. These results signify that Cs2SnI2Cl2and Cs2PbI2Cl2monolayers are promising thermoelectric candidates.