Valence Band Structure Degeneracy Enhanced Thermoelectric Performance in β-Cu<sub>2</sub>Se
Xiaomeng Cai, Huirong Jing, Hexige Wuliji, Hong Zhu
Abstract
Cu 2 Se is known to be a promising p-type thermoelectric material resulting from its extremely low thermal conductivity. On the other hand, compared to other high-performance thermoelectric materials like PbTe, the valence band degeneracy of Cu 2 Se is 4 times lower, which is believed to be unfavorable to the power factor. In this work, band structure engineering has been applied to increase the band degeneracy of Cu 2 Se through effective doping. Based on the careful analysis of bonding characters and atomic energy levels in the Cu 2 Se compound, some defects (the Fe or Mn substitutional defects, Fe Cu or Mn Cu, and the copper vacancy, V Cu ) are predicted to be able to converge two valence band maxima in Cu 2 Se. The electrical transport properties of Cu 2 Se with different defects (V Cu /Fe Cu /Mn Cu ) have been studied based on first-principles electronic structure calculations. A Boltzmann transport study demonstrates that the weakened p–d orbital interaction may enhance the electrical transport properties in Cu 2 Se.