Extremely high thermoelectric performance of SnSe at optimal carrier densities*

High-efficiency thermoelectric materials are desirable for their capability of functioning as all solid-state modules for electric power generation from waste heat or distributed spot-size refrigeration. Bulk tin selenide (SnSe) has received much attention since its excellent thermoelectric figure of merit (zT) was reported. Using extensive first-principles calculations of carrier-impurity and carrier-phonon scattering processes, we investigate the optimal carrier densities to maximize zT in p- and n-doped SnSe over a broad range of temperatures. We predict an ultrahigh zT > 4 for in-plane p-doped and out-of-plane n-doped SnSe at high temperatures, which is robust against variations in the concentration of ionized impurities. An extensive analysis of the transport properties as a function of the carrier density and temperature indicates that the Lorenz number reaches a minimum at the optimal conditions. Our results are motivation for improving the efficiency of doping in SnSe in order to attain optimal carrier densities.