Interface‐Enhanced High‐Temperature Thermoelectricity in Cu1.99Se/B₄C Composites with Synergistically Improved Mechanical Strength

Degenerate semiconductors usually demonstrate a metallic‐like conduction behavior, showing limited carrier mobility at high temperatures. Herein, by incorporating B 4 C nanoparticles into the Cu 1.99 Se system, an unusual switch from the “degenerate” to “non‐degenerate” semiconducting behavior is revealed as a result of the engineered interfaces. Heterogeneous interfaces and disordered Cu 2 Se amorphous phases are introduced in the Cu 1.99 Se/B 4 C composites, which generate a trapping effect against the mobile Cu ions, leading to a distinctive “hump” signature for electrical conductivity. Benefiting from this rare high‐temperature thermoelectric response, a high power factor is obtained due to reduced carrier concentration and enhanced mobility, and low lattice thermal conductivity is retained because of relatively stronger anharmonic lattice vibrations. Consequently, the Cu 1.99 Se + 0.9 vol.% B 4 C sample at least achieves a maximum thermoelectric figure of merit ( ZT ) of 2.6 at 1025 K with synergistically enhanced mechanical robustness. The present interface engineering strategy may be applicable to other thermoelectric materials with ionic migration characteristics.