Thermoelectric Optimization of n-Type AgBiSe₂ via Se Vacancy Control and Transition-Metal Doping

Silver bismuth selenide (AgBiSe 2 ) has garnered attention as a Pb-free material with a high thermoelectric efficiency owing to its intrinsically low thermal conductivity. Although pristine AgBiSe 2 is an n-type material, in this study, a weak p-type intrinsic property is achieved in AgBiSe 2 owing to the high sensitivity of its carrier type and concentration to Se vacancies. Herein, we report the enhancement of the thermoelectric performance of AgBiSe 2 by introducing Se vacancies and aliovalent transition-metal doping at the Ag site. Se vacancies are first introduced to switch the conductivity of AgBiSe 2 to the n-type and considerably increase the carrier concentration. Further, aliovalent transition-metal dopants are incorporated to tune the carrier concentration and thus increase the electrical conductivity of AgBiSe 2 . The electrical mobility and effective mass are also increased, which improves the electrical properties and enhances the power factor. The Ag 0.97 Cd 0.03 BiSe 1.995 sample exhibited the highest dimensionless figure of merit ( zT max ) of ∼0.65 at 773 K and an average dimensionless zT avg of ∼0.39 between 323 and 773 K.