Minimal twin structures enabling extraordinary thermoelectric power factor of n-type Bi₂Te₃ thin films

Boosting carrier mobility is essential for achieving high room-temperature thermoelectric performance in n-type Bi₂Te₃-based films, which have long exhibited inferior power factors compared with their single crystal counterparts due to poor carrier mobility. To overcome this challenge, we develop a simple substrate surface engineering strategy to fabricate Twin-free n-type Bi₂Te₃ (000 l) thin films. Atomic-scale analyses and transport measurements uncover that eliminating twin structures avoids twin-induced band bending and severe lattice strain, enabling the simultaneously enhanced carrier mobility and suppressed bipolar conduction. The optimized Twin-free Bi₂Te₃ film exhibits a high room-temperature carrier mobility of ~279 cm²V^-1 s^-1, doubling the mobility of films containing twin structures, and consequently achieves an extraordinary room-temperature power factor of ~6.17 mW m^-1 K^-2. These findings highlight the critical role of minimizing twin structures in boosting the carrier mobility and mitigating bipolar conduction, thereby providing an effective route toward high-performance thermoelectric thin films.