Ultralow thermal conductivity and high ZT of Cu2Se-based thermoelectric materials mediated by TiO2−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 TiO2−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 TiO2−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.