Conduction Band Convergence and Modular Nanostructures: Driving High Thermoelectric Performance in n‐Type PbSe

Abstract n ‐type lead chalcogenides showing high thermoelectric performance are rare due to the larger energy offset between the two lowest energy conduction bands minima, leaving ample opportunity to modulate electronic structure for improving their thermoelectric performance. Here, we present a remarkable thermoelectric figure of merit (zT) of ∼1.8 at 873 K in n ‐type PbSe doped with MoCl 5 by modulation of the conduction bands, while simultaneously suppressing the phonon transport. Doping MoCl 5 in PbSe induces notable convergence of conduction bands and an increased density of states near the Fermi level, mainly due to the contribution of Mo 4 d orbital hybridized with the Se 4 p ‐Pb 6 p . This results in an improved Seebeck coefficient, despite maintaining a high n ‐type charge carrier concentration resulting in an excellent power factor (σS 2 ) of ∼21 µW cm −1 K −2 at 873 K for PbSe + 1 mol% MoCl 5 . When the solid solution limit of the doping exceeds, it forms unique modular nano‐heterostructures (5‐30 nm) of PbSe‐MoSe 2 misfit layered compounds embedded in PbSe matrix. These nano‐heterostructures significantly intensify phonon scattering, leading to an ultralow lattice thermal conductivity (κ lat ) of 0.20 W m −1 K −1 at ∼725 K in PbSe + 1 mol% MoCl 5 sample.