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 cm2 V-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. The substrate surface engineering approach prevents the formation of twin structures, while the elimination of twins greatly enhances carrier mobility and suppresses bipolar conduction, leading to optimized power factor in twin-free Bi2Te3 films.