Enhanced thermoelectric performance in p-type AgBiSe₂ through carrier concentration optimization and valence band modification

Realizing the high thermoelectric performance of p-type AgBiSe₂-based materials has been challenging due to their low p-type dopability. This work demonstrated that Cd doping at the Bi site converts n-type AgBiSe₂ to p-type. The hole concentration is effectively increased with increasing Cd doping content, thereby enhancing the electrical conductivity. Theoretical calculations reveal that Cd doping flattens the edge of the valence band, resulting in an increase in the density-of-states effective mass and Seebeck coefficient. A record-high power factor of ~ 6.2 µW⋅cm⁻¹⋅K⁻² was achieved at room temperature. Furthermore, the induced dislocations enhance the phonon scattering, contributing to the ultralow lattice thermal conductivity across the entire temperature range. As a result, a decent figure of merit (zT) of ~ 0.3 at room temperature and a peak zT of ~ 0.5 at 443 K were obtained in AgBi_0.92Cd_0.08Se₂. Our work provides a feasible method for optimizing the thermoelectric performance of p-type AgBiSe₂.