Improved Thermoelectric Performance in Cu-Based Ternary Chalcogenides Using S for Se Substitution

Cu-based ternary chalcogenide semiconductors are a promising class of p-type thermoelectric materials. Here we show that S for Se substitution is a promising route for improving the thermoelectric performance of these compounds, in particular for Cu₃SbSe₄ and Cu₂SnSe₃. Phonon scattering due to the combined effects of the atomic mass and size difference between S and Se produces a significant reduction in lattice thermal conductivity over a wide temperature range, and limits the phonon mean free path to its minimum possible value at high temperature. The small electronegativity difference between S and Se is ideal for conserving carrier mobility, as demonstrated by the reasonably large hole mobility in the disordered Cu₃Sb(Se_1−x S _x )₄ compounds. These effects along with the low-cost, environmentally benign nature of S, make S for Se substitution a simple yet effective method of improving the thermoelectric performance of Cu-based ternary selenides.