  Although there are enormous numbers of high-temperature thermoelectric
materials present, designing a near-room-temperature especially n-type
thermoelectric material with high zT is extremely challenging. Generally,
pristine Ag2Se exhibits unusual low thermal conductivity along with high
electrical conductivity and Seebeck coefficient, which leads to high
thermoelectric performance (n-type) at room temperature. Herein, we report a
pseudoternary phase, Ag2Se0.5Te0.25S0.25, which shows improved thermoelectric
performance (zT ~ 2.1 at 400 K). Density functional theory reveals that the
Rashba type of spin-dependent band spitting originated because of Te-doping,
enhancing carrier mobility. Using density functional perturbation theory, we
hereby realize that the intrinsic carrier mobility is not only controlled by
carrier effective mass, neither deformation potential theory, instead it is
substantially limited by longitudinal optical phonon scattering. In fact,
locally off-centered S atoms and rising configurational entropy via
substitution of Te and S atoms in Ag2Se significantly reduce the lattice
thermal conductivity (klat ~ 0.34 at 400 K). In order to accurately obtain
electrical as well as thermal transport coefficient, we adopt deformation
potential theory based on Boltzmann transport formalism. The combined
consequence of the Rashba effect coupled with configurational entropy
synergistically results in such high thermoelectric performance with the
development of new n-type thermoelectric material working at the
near-room-temperature regime.
