Ultrahigh Power Factor of Sputtered Nanocrystalline N‐Type Bi₂Te₃ Thin Film via Vacancy Defect Modulation and Ti Additives

Abstract

Magnetron‐sputtered thermoelectric thin films have the potential for reproducibility and scalability. However, lattice mismatch during sputtering can lead to increased defects in the epitaxial layer, which poses a significant challenge to improving their thermoelectric performance. In this work, nanocrystalline n‐type Bi2Te3 thin films with an average grain size of ≈110 nm are prepared using high‐temperature sputtering and post‐annealing. Herein, it is demonstrated that high‐temperature treatment exacerbates Te evaporation, creating Te vacancies and electron‐like effects. Annealing improves crystallinity, increases grain size, and reduces defects, which significantly increases carrier mobility. Furthermore, the pre‐deposited Ti additives are ionized at high temperatures and partially diffused into Bi2Te3, resulting in a Ti doping effect that increases the carrier concentration. Overall, the 1 µm thick n‐type Bi2Te3 thin film exhibits a room temperature resistivity as low as 3.56 × 10−6 Ω∙m. Notably, a 5 µm thick Bi2Te3 thin film achieves a record power factor of 6.66 mW mK−2 at room temperature, which is the highest value reported to date for n‐type Bi2Te3 thin films using magnetron sputtering. This work demonstrates the potential for large‐scale of high‐quality Bi2Te3‐based thin films and devices for room‐temperature TE applications.