Decoupling Carrier Concentration and Mobility in Hot-Extruded n-Type Bismuth Telluride for Enhanced Thermoelectric Performance

Abstract Bi2Te3-based materials have attracted considerable attention due to their excellent thermoelectric performance at room temperature. However, the pulverization process during fabrication tends to introduce the donor-like effect, which significantly increases the carrier concentration and consequently degrades the room-temperature thermoelectric properties, especially for n-type Bi2Te3-based materials. In this study, decoupling of carrier concentration and mobility was achieved by a two-step heat treatment combined with hot extrusion. During the pre-annealing process, Te vacancies were introduced into the lattice by controlling Te volatilization, and Bi atoms migrated into these vacancies, generating holes and thereby reducing the carrier concentration. The post-annealing temperature exhibited a negligible influence on the carrier concentration but substantially improved the carrier mobility. The hot-extruded Bi2Te2.8Se0.2 sample with a two-step treatment achieved the optimized carrier concentration and the enhanced mobility. As a result, a maximum zT of 1.13 was achieved at 350 K, marking a nearly 40% enhancement compared with the directly extruded sample. This performance substantially exceeds the typical values reported for n-type Bi2Te3-based materials via other processing routes, demonstrating that our strategy offers an effective route to decouple carrier concentration and mobility and thereby enhance thermoelectric performance. This work thus provides a practical and scalable pathway for waste-heat recovery and near-room-temperature cooling applications.