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

Context & scaleThermoelectric materials enable the direct conversion from heat into electricity for power generation, contributing to resolving the worldwide energy and environmental crises simultaneously. Cu2Se is rendered as a promising candidate for high-temperature thermoelectric applications. Despite noticeable advances in electrical transport modulation, very limited room is left for thermal transport optimization, mainly due to the presence of intrinsic Cu vacancies, liquid-like features of Cu ions, and low elemental solubility in the crystal lattice. Herein, we propose a facile nanocomposite strategy to optimize the thermal transport by modifying TiO2−n self-assemblies. These sophisticated TiO2−n architectures can not only reduce carrier concentration without degrading mobility but also generate huge thermal resistance. Consequently, an ultralow total thermal conductivity of 0.285 WK−1m−1 is achieved in the TiO2−n-added sample, leading to a high ZT value of 2.8 at 973 K.Highlights•P-N junctions lower carrier concentration without degrading carrier mobility•An ultralow total thermal conductivity of 0.285 WK−1m−1 is achieved at 973 K•TiO2−n addition contributes to a peak ZT of 2.8 at 973 K•TiO2−n architectures are systematically characterized by Cs-corrected STEMSummaryCu2Se 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.Graphical abstract