Thermoelectric performance in Ag2Se nanocomposites: The role of interstitial Ag and Pb orbital hybridization

Ag 2 Se has emerged as a promising thermoelectric (TE) material for room-temperature applications. However, its TE performance is limited by the low carrier effective mass ( m* ) of only 0.1  m 0 , where m 0 represents the free electron mass. In this study, we employ a microwave-assisted method to synthesize nanostructured Ag 2-x Se with Pb doping that is found to increase m* to 0.4  m 0 . Accordingly, the Seebeck coefficient is significantly enhanced, which together with the high electrical conductivity, leads to enhanced electronic transport. The increase in m* is systematically investigated by density functional theory calculations and linked to the enhanced electronic by modeling simulations. The calculated band structures reveal that the hybridization of heavy Pb-6p orbitals flattens the conduction band edges, and thereby enhances m* . Furthermore, Pb doping significantly reduces the lattice thermal conductivity due to the high-density point defects, dislocations, and grain boundaries, as revealed by detailed electron microscopy characterizations. The synergy from both enhanced electronic transport and reduced phonon propagation yielded a maximum figure of merit of 1.04 at 376 K, and an average figure of merit of 1.0 for Pb-doped Ag 1.9 Se. The optimized TE performance is further validated in a flexible TE generator, which produced a maximum output power of 0.6 μW at a temperature difference of 45 K. These findings demonstrate that enhancing m* and increasing phonon-scattering using vacancy tuning and aliovalent doping effectively boosts the TE performance of Ag 2 Se, a strategy that can be extended to other TE materials to maximize their potentials for power generation and thermoelectric cooling applications.