Ultralow thermal conductivity and high ZT of Cu₂Se-based thermoelectric materials mediated by TiO_2−n nanoclusters

Cu₂Se is a promising p-type thermoelectric material for energy harvesting due to its intrinsically low thermal conductivity arising from the liquid-like Cu ions, leaving very limited room for regulation of phonon propagation. Herein, the thermal conductivity of superionic Cu₂Se is efficiently mediated by titanium oxide nanoclusters, leading to an exceptionally high thermoelectric figure of merit (ZT) at high temperatures. By controlling the oxygen deficiency, the sophisticated TiO_2−n architectures can be constructed with optimized phase composition and electrical properties. The presence of p-n junctions helps to reduce carrier concentration without degrading mobility, and the complex heterogeneous interfaces generated by TiO_2−n nanoclusters give rise to huge interfacial thermal resistance. Benefiting from the suppressed electrical transport and enhanced phonon scattering, the total thermal conductivity shows a reduction of at least 36%, contributing to a high ZT value of 2.8 at 973 K. This work demonstrates a paradigm of modulating thermal transport through the self-assembly design.