Identifying the Origins of High Thermoelectric Performance in Group IIIA Element Doped PbS

In this study, the thermoelectric properties of group IIIA element (Al, Ga, In) doped PbS are systematically investigated. Al shows a low solubility limit (<1 mol %) in PbS, whereas Ga and In are soluble up to 2 mol %. Both experimental results and theoretical calculations suggest that Ga or In doping introduces strong gap states in PbS, which are the physical origins of enhanced effective mass and Seebeck coefficients. Meanwhile, a subtle simulation of carrier-concentration-dependent mobilities under single Kane band model clearly reveals that Ga doping significantly lowers the deformation potential of n-type PbS, whereas In does not. This lower deformation potential yields higher electrical conductivities at the same doping levels. The weakened electron phonon coupling phenomenon by Ga doping in PbS is further verified by our first-principles calculations. The rare combination of large effective mass and low deformation potential in Ga-doped PbS contributes to a high ZT value of ∼0.9 at 723 K, ∼50% higher than that of Cl-doped PbS control sample.