Two-Dimensional WSe2/SnSe p-n Junctions Secure Ultrahigh Thermoelectric Performance in n-type Pb/I Co-doped Polycrystalline SnSe

Abstract In this study, we, for the first time, introduce p-type two-dimensional (2D) WSe2 nanoinclusions in n-type Pb/I co-doped SnSe matrix to form WSe2/SnSe p-n junctions. These p-n junctions act as energy barriers and effective phonon scattering sources, leading to a high figure-of-merit (ZT) of ∼1.35 at ∼790 K in n-type polycrystalline SnSe. First-principles density functional theory calculation results indicates that I-doping shifts Fermi level up into conduction bands of SnSe, making the system n-type behavior, while both Pb and I dopants act as point-defect-based short-wavelength phonon scattering centers. The introduced p-type 2D WSe2 nanoinclusions induce high-density WSe2/SnSe interfaces that act as p-n junctions, which block the electron carriers and rationally tune the carrier density, contributing to a high absolute Seebeck coefficient of ∼470.7 μV K-1 and a high power factor of ∼5.9 μW cm-1 K-2. Meanwhile, the dense phase boundaries and considerable lattice strains by the introduced 2D WSe2 nanoinclusions significantly strengthen the mid- and long-wavelength phonon scattering, giving rise to a much low thermal conductivity of 0.35 W m-1 K-1 and in turn a high ZT of ∼1.35. This study provides a new strategy to achieve high thermoelectric performance in n-type polycrystalline SnSe.