Defect structure regulation and thermoelectric transfer performance in n-type Bi2-xSbxTe3-ySey-based compounds

Bi2Te3-based compounds are thermoelectric materials with the best performance near room temperature. The existence of a large number of complex defects makes defect engineering a core stratagem for adjusting and improving the thermoelectric performance. Therefore, understanding and effectively controlling the existence form and concentration of defects is crucial for achieving high-thermoelectric performance in Bi2Te3-based alloy. Herein, a series of Cl doped n-type quaternary Bi2-xSbxTe3-ySey compounds is synthesized by the zone-melting method. The correlation between defect evolution process and thermoelectric performance is systematically investigated by first-principles calculation and experiments. Alloying Sb on Bi site and Se on Te site induce charged structural defects, leading to a significant change in the carrier concentration. For Bi2-xSbxTe2.994Cl0.006 compounds, alloying Sb on Bi site reduces the formation energy of the antisite defect, which generates the antisite defect and accompanied with the increase of the minority carrier concentration from 2.09x10(16) to 3.99x10(17) cm(-3). The increase of the minority carrier severely deteriorates the electrical transport properties. In contrast, alloying Se in the Bi1.8Sb0.2Te2.994-ySeyCl0.006 compound significantly lowers the formation energy of the complex defect +, which becomes more energetically favorable and suppresses the formation of the antisite defect. As a result, the concentration of minority carriers decreases to 1.46x10(16) cm(-3). This eliminates the deterioration effect of the minority carrier on the electrical transport properties of the material and greatly improves the power factor. A maximum power factor of 4.49 mW/(m center dot K-2) is achieved for Bi1.8Sb0.2Te2.944Se0.05Cl0.006 compound at room temperature. By reducing thermal conductivity through intensifying the phonon scattering via alloying Sb and Se, the maximum ZT value of 0.98 is attained for Bi1.8Sb0.2Te2.844Se0.15Cl0.006 compound at room temperature. Our finding provides an important guidance for adjusting point defects, carrier concentrations, and thermoelectric performances in Bi2Te3-based compounds with complex compositions.