Cu‐In Co‐Doping and Layered Directional Sintering for High Thermoelectric Efficiency and Mechanical Strength in Bi ₂ (Te,Se) ₃

Abstract Bi ₂ Te ₃ ‐based thermoelectric materials are essential for efficient power generation, but limitations in the performance of n‐type Bi ₂ Te _2.7 Se _0.3 (BTS) restrict broader applications. Advancing n‐type BTS thermoelectric properties is challenging due to the need to reduce lattice thermal conductivity while simultaneously enhancing carrier mobility and mechanical strength. In this study, these challenges are addressed by combining Cu intercalation, In doping, and a novel Layered Directional Sintering (LDS) technique. Cu intercalation increases carrier concentration and raises the density of states near the Fermi level through band flattening induced by internal stress, while In doping widens the bandgap and introduces additional states near the Fermi level. The LDS method further improves thermoelectric efficiency by creating highly textured grains, dense dislocations, and nanostructures, which collectively lower lattice thermal conductivity. This integrated approach achieves a peak ZT of 1.2 at 375 K and an average ZT of 1.1 over 325–525 K, outperforming previous benchmarks for n‐type BTS and providing mechanical strength 2–3 times that of commercial BTS. This study establishes a framework to balance thermal conductivity and carrier mobility, potentially enhancing efficiency in a broader range of thermoelectric materials.