Enhanced thermoelectric performance of Cu2Se through Cu-deficiency and Te-substitution

Abstract

Copper selenide (Cu₂Se), a phonon liquid electron crystal (PLEC), is a promising thermoelectric material due to its efficient electron transport, but it suffers from copper ion migration, compromising its chemical stability. In this study, we explore the role of controlled copper deficiency in modifying the Cu ion environment. Nudged elastic band (NEB) calculations reveal that tellurium (Te) substitution increases the Cu-ion migration energy barrier from 0.35 eV to 0.50 eV, improving structural robustness. Selenium (Se) is strategically substituted with tellurium (Te), enhancing carrier mobility, as demonstrated by single-band effective mass calculations using density functional theory (DFT) supported by Hall measurements. Additionally, Te-substitution introduces low-energy optical phonons and dislocations, intensifying acoustic phonon scattering and reducing lattice thermal conductivity. The deviation of specific heat capacity (C_p) from the Dulong–Petit limit confirms disrupted heat capacity behavior, enhancing thermal insulation. These effects yield a peak zT of 1.98 at 975 K with 20 wt% Te. The fabricated module achieved 52 mW power output under ΔT = 670 K, advancing Cu₂Se thermoelectrics for sustainable applications.