Dense dislocations enable high-performance PbSe thermoelectric at low-medium temperatures

Abstract

PbSe-based thermoelectric materials exhibit promising ZT values at medium temperature, but its near-room-temperature thermoelectric properties are overlooked, thus restricting its average ZT (ZT_ave) value at low-medium temperatures. Here, a high ZT_ave of 0.90 at low temperature (300-573 K) is reported in n-type PbSe-based thermoelectric material (Pb_1.02Se_0.72Te_0.20S_0.08-0.3%Cu), resulting in a large ZT_ave of 0.96 at low-medium temperatures (300-773 K). This high thermoelectric performance stems from its ultralow lattice thermal conductivity caused by dense dislocations through heavy Te/S alloying and Cu interstitial doping. The dislocation density evaluated by modified Williamson-Hall method reaches up to 5.4 × 10¹⁶ m^-2 in Pb_1.02Se_0.72Te_0.20S_0.08-0.3%Cu. Moreover, the microstructure observation further uncloses two kinds of dislocations, namely screw and edge dislocations, with several to hundreds of nanometers scale in length. These dislocations in lattice can strongly intensify phonon scattering to minimize the lattice thermal conductivity and simultaneously maintain high carrier transport. As a result, with the reduced lattice thermal conductivity and optimized power factor in Pb_1.02Se_0.72Te_0.20S_0.08-0.3%Cu, its near-room-temperature thermoelectric performance is largely enhanced and exceeds previous PbSe-based thermoelectric materials.