Boosting the thermoelectric performance of PbSe through dynamic doping and hierarchical phonon scattering

Here we find the peculiar behavior of Cu ions in the PbSe-Cu system increases its thermoelectric performance. For the electrical transport, a dynamic doping effect is achieved because more Cu ions enter into the PbSe lattice and provide extra charge carriers as the temperature increases, which guarantees an optimized carrier concentration over a wide temperature range. For the thermal transport, the presence of Cu2Se nanoprecipitates and dislocations at a low temperature range as well as the vibration of Cu atoms around the interstitial sites of PbSe at high temperatures result in hierarchical phonon scattering and a significantly reduced lattice thermal conductivity over the whole temperature range. As a result, a peak thermoelectric material figure of merit zT of up to 1.45 and a thermoelectric device figure of merit ZT close to unity are obtained for the sample with 0.375 at% Cu. Furthermore, enhanced thermoelectric properties are also realized for the Cu-intercalated PbS, implying that the temperature-driven dynamic behavior of Cu ions in a rigid lattice can serve as a general strategy to optimize the thermoelectric performance of IV-VI compounds.