Contrasting thermoelectric transport behaviors of p-type PbS caused by doping alkali metals (Li and Na)

PbS is a latent substitute of PbTe thermoelectric materials, which is on account of its superiority in low cost and earth abundance. Here, the thermoelectric transport properties of p-type PbS by doping alkali metals (Na and Li) are investigated and it is verified that Li is a more effective dopant than Na. By introducing Li, the electrical and thermal transport properties were optimized collectively. The electrical transport properties were boosted remarkably via adjusting carrier concentration, and the maximum power factor (PFmax) of ~11.5 μW/cmK2 and average power factor (PFave) ~9.9 μW/cmK2 between 423 and 730 K in Pb0.99Li0.01S were achieved, which are much higher than those (~9.5 and ~7.7 μW/cmK2) of Pb0.99Na0.01S. Doping Li and Na can weaken the lattice thermal conductivity effectively. Combining the enlarged PF with suppressed total thermal conductivity, a maximum ZT ~0.5 at 730 K and a large average ZT ~0.4 at 423-730K were obtained in p-type Pb0.99Li0.01S, which are higher than ~0.4 and ~0.3 in p-type Pb0.99Na0.01S, respectively.