Multifunctions of Mo in PbS Matrix Leading to Superior Thermoelectric Performance

PbS is a promising thermoelectric material because its band and crystal structures are similar to those of PbTe, as well as for its practical advantages of low cost and high melting point. However, the lower power factor and high lattice thermal conductivity result in suboptimal thermoelectric performance. In this study, we demonstrated that the low‐solid‐solubility Mo undergoes a variety of chemical reactions in the PbS matrix due to the formation of multiple precipitates (MoS 2 , Sb, and Pb). In addition, the Mo doping can reduce cation vacancies, facilitate lattice plainification, and improve carrier mobility. Consequently, the average power factor exhibits an enhancement from 11.7 µW cm ‒1 K ‒2 for Pb 0.985 Sb 0.015 S to 15.6 µW cm ‒1 K ‒2 for Pb 0.965 Sb 0.015 Mo 0.02 S. Then, Se‐alloying further introduces point defects, which intensifies the phonon scattering. As a result, the Pb 0.965 Sb 0.015 Mo 0.02 S 0.8 Se 0.2 achieved a peak ZT of 1.2 at 923 K. Moreover, the average ZT of 0.76 from 400 to 923 K is one of the state‐of‐the‐art values in PbS‐based materials. Furthermore, the fabricated single‐leg device achieved a conversion efficiency of 5.8% at a temperature difference of 551 K. These results indicate that introducing low‐solid‐solubility and highly reactive elements into the matrix is a promising approach to improving thermoelectric properties.