Enhanced Thermoelectric Performance and Electronic Transport Properties of Ag-Doped Cu_{2- x}S_0.5Se_0.5

In addition to eco-friendliness and low raw material cost, Cu2S0.5Se0.5 exhibits promising middle-to-high-temperature thermoelectric performance by the virtue of the coexistence of liquid-like phonon transport and electron crystal-like charge transport. Toward higher thermoelectric performance, however, in-depth studies of the electrical conduction mechanism are scarce. Herein, we investigate the electrical transport mechanism and improve the thermoelectric performance of Cu2S0.5Se0.5 by introducing Cu vacancies and substituting Cu with Ag. An optimized electronic quality factor in conjunction with a reduced lattice thermal conductivity leads to a state-of-the-art figure of merit zT ∼1.23 at 773 K and an average zT ∼0.47 between 295 and 773 K in Ag0.02Cu1.955S0.5Se0.5.