Enhancement of Thermoelectric Performance for n-type PbS through Synergy of Gap State and Fermi Level Pinning

We report that Ga-doped and Ga-In co-doped n-type PbS samples show excellent thermoelectric performance in the intermediate temperature range. First-principles electronic structure calculations reveal that Ga doping can cause Fermi level pinning in PbS by introducing a gap state between the conduction and valence bands. Furthermore, Ga-In co-doping introduces an extra conduction band. These added electronic features lead to high electron mobilities up to µH ~630 cm2V−1s−1 for n of 1.67 × 1019 cm−3 and significantly enhanced Seebeck coefficients in PbS. Consequently, we obtained a maximum power factor of ~32 Wcm−1K−2 at 300 K for Pb0.9875Ga0.0125S, which is the highest reported for PbS-based systems giving a room-temperature figure of merit, ZT of ~0.35 and ~0.82 at 923 K. For the co-doped Pb0.9865Ga0.0125In0.001S the maximum ZT rises to ~1.0 at 923 K and achieves a record-high average ZT (ZTavg) of ~0.74 in the temperature range of 400 K to 923 K.