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

Luo, Zhong-Zhen, Hao, Shiqiang, Cai, Songting, Bailey, Trevor P., Tan, Gangjian, Luo, Yubo, Spanopoulos, Ioannis, Uher, Ctirad, Wolverton, Chris, Dravid, Vinayak P., Yan, Qingyu, Kanatzidis, Mercouri G.
Journal of the American Chemical Society 2019 v.141 no.15 pp. 6403-6412
ambient temperature, gallium
We report that Ga-doped and Ga–In-codoped 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 codoping introduces an extra conduction band. These added electronic features lead to high electron mobilities up to μH ∼ 630 cm² V–¹ s–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 μW cm–¹ K–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 codoped 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 400–923 K.