Band Sharpening and Band Alignment Enable High Quality Factor to Enhance Thermoelectric Performance in n-Type PbS

Low-cost and earth-abundant PbS-based thermoelectrics are expected to be an alternative for PbTe, and have attracted extensive attentions from thermoelectric community. Herein, a maximum ZT (ZT_max) ≈ 1.3 at 923 K in n-type PbS is obtained through synergistically optimizing quality factor with Sn alloying and PbTe phase incorporation. It is found that Sn alloying in PbS can sharpen the conduction band shape to balance the contradictory interrelationship between carrier mobility and effective mass, accordingly, a peak power factor of ∼19.8 μWcm^-1K^-2 is achieved. Besides band sharpening, Sn alloying can also narrow the band gap of PbS so as to make the conduction band position between Pb_0.94Sn_0.06S and PbTe well aligned, which can benefit high carrier mobility. Therefore, incorporating the PbTe phase into the Pb_0.94Sn_0.06S matrix can not only favorably maintain the carrier mobility at ∼150 cm²V^-1s^-1 but also suppress the lattice thermal conductivity to ∼0.61 Wm^-1K^-1 in Pb_0.94Sn_0.06S-8%PbTe, which contributes to a largely enhanced quality factor. Consequently, an average ZT (ZT_ave) ≈ 0.72 in 300-923 K is achieved in Pb_0.94Sn_0.06S-8%PbTe that outperforms other n-type PbS-based thermoelectric materials.