Enhanced power factor in n-type PbS across the topological phase transition

As a member of the rocksalt lead chalcogenides, PbS with chemical stability and Earth-abundant sulfur holds great promise to exhibit comparable thermoelectric performance as its sister compounds PbTe and PbSe. Owning to their similar thermal transport behavior, increasing the electrical properties of PbS becomes a goal in the thermoelectrical study. By choosing Ga-doped PbS, we perform high-pressure measurements of the structural and electrical properties. The significant enhancement of the thermoelectric power factor of 61 µW cm⁻¹ K⁻² at room temperature is obtained at pressure of around 2.2 GPa. This notable improvement is found to stem from the dramatic increase in the Seebeck coefficient, without sacrificing the electrical conductivity. Such an enhancement is proposed to be related to the topological phase transition from a trivial state (narrow band gap semiconductor) to a topologically nontrivial state (topological crystalline insulator). This discovery underscores the potential benefits of approaching the topological state for further enhancing thermoelectric performance.