Lattice plainification and high symmetry enhance the thermoelectric performance of n-type Bi2Te3-based materials

Abstract

Thermoelectric materials, which enable direct solid-state conversion between heat and electricity, are promising for applications in refrigeration and power generation. Bi₂Te₃-based thermoelectric materials have achieved commercialization due to their superior performance and mature device fabrication technology. However, the further development of Bi₂Te₃-based devices is hampered by the performance shortcomings of n-type compositions. Therefore, enhancing the performance of n-type Bi₂Te₃ is crucial for advancing practical thermoelectric technology. In this work, we collaboratively employed Se alloying at the Te site and interstitial In doping to decouple electrical transport in n-type Bi₂Te₃. We used a specific bond angle to evaluate the local lattice symmetry in Bi₂Te₃ and explained the increase in carrier mobility. First-principles calculations were also carried out to confirm the resonant level induced by In doping. Thereby, we realized the collaborative optimization of carrier mobility and effective mass to yield a high-performance n-type Bi₂Te₃ with a maximum thermoelectric figure of merit of ∼1.1 at 300 K and an average ZT_ave of ∼1.1 over the 300–373 K range. Furthermore, we fabricated a single-leg device based on the optimized n-type Bi₂Te₃ alloys and obtained a high conversion efficiency of 5.3% under a temperature difference of 225 K. This work provides a solution for improving the performance of n-type Bi₂Te₃ and, more importantly, proposes an indicator of the local lattice symmetry in Bi₂Te₃. This indicator shows promise as an effective tool for studying the relationship between local lattice symmetry and carrier mobility in Bi₂Te₃ and even potentially in other thermoelectric material systems.