Grain Manipulation by Annealing Treatment Realizes High‐Performance N‐Type Bi₂Te_2.4Se_0.6 Thermoelectric Material and Device

Bi₂Te₃‐based materials play a crucial role in solid cooling and power generation, but the rapidly deteriorated ZT with rising temperatures above 450 K severely limits further applications. Here, this paper reports a novel preparation method of annealing treatment for molten ingot, which can enhance the thermoelectric performance of n‐type Bi₂Te_2.4Se_0.6 in a wide temperature range. Instead of conventional halides, copper is adopted to regulate the carrier concentration and grain size to optimal levels. During the process of annealing at 573 K for 4 h, the number of twins significantly increases and the grains of Cu‐doped samples become larger and more oriented. These optimizations lead to higher carrier mobility with similar carrier concentration compared with the sample without heat treatment. The synergistic effects of Cu doping and annealing treatment realize a high average ZT of 0.89 within 300–600 K in n‐type Cu_0.02Bi₂Te_2.4Se_0.6. Combined with p‐type (Bi,Sb)₂Te₃, the fabricated thermoelectric device exhibits a high conversion efficiency of 6.9% at a temperature difference of 300 K. This study suggests that annealing treatment is a simple and effective scheme to promote the applications of n‐type Bi₂(Te,Se)₃ in a wide temperature range.