Advancing thermoelectrics by suppressing deep-level defects in Pb-doped AgCrSe₂ alloys

Abstract AgCrSe2-based compounds have attracted much attention as an environmentally friendly thermoelectric material in recent years due to the intriguing liquid-like properties. However, the ultra-low carrier concentration and the high AgCr deep-level defects limit the overall thermoelectric performance. Here, we successfully introduced Pb into Ag-deficient Ag0.97CrSe2 alloys to tune the carrier concentration across a broad temperature range. The Pb2+ as an acceptor dopant preferentially occupies Cr sites, boosting the hole carrier concentration to 1.77×1019 cm-3 at room temperature. Furthermore, the Pb strongly inhibited the creation of intrinsic AgCr defects, weakened the increased thermal excited ionization with the increasing temperature and slowed the rising trend of carrier concentration. The designed carrier concentration matches the theoretically predicted optimized one over the entire temperature range, leading to a remarkable enhancement in power factor, especially the maximum power factor of ~500 μW·m-1·K-2 at 750 K is superior to most previous results. Additionally, the abundant point defects promote phonon scattering, thus reducing the lattice thermal conductivity. As a result, the maximum figure of merit zT (~0.51 at 750 K) is achieved in Ag0.97Cr0.995Pb0.005Se2. This work confirms the feasibility of manipulating deep-level defects to achieve temperature-dependent optimal carrier concentration and provides a valuable guidance for other thermoelectric materials.