Partial indium solubility induces chemical stability and colossal thermoelectric figure of merit in Cu2Se

Abstract

High thermoelectric figure of merit, ZT ∼ 2.1 at 1000 K, have been reported in Cu_2−xSe-based materials. However, their deployments in operational devices have been hampered by chemical instability and low average ZT (ZT_ave) values. Here, we demonstrate improved chemical stability and a record high ZT_ave ∼ 1.5 over a broad temperature range (T ≤ 850 K) in Cu₂Se/CuInSe₂ nanocomposites, with ZT values ranging from 0.6 at 450 K to an unprecedentedly large value of 2.6 at 850 K for the sample with 1 mol% In. This remarkable performance is attributed to the localization of Cu⁺ ions induced by the incorporation of In into the Cu₂Se lattice, which simultaneously boost the electrical conductivity and reduce the thermal conductivity of the nanocomposites. These findings pave the way for large-scale utilization of Cu₂Se-based materials in thermoelectric generators.