Role of O and Se defects in the thermoelectric properties of bismuth oxide selenide

摘要

Bismuth oxygen selenide, Bi_2O_2Se, is a promising thermoelectric material because of its reduced thermal conductivity. In this study, we perform the first-principles calculation and utilize the solution of Boltzmann transport equation in a constant relaxation-time approximation to compute the electronic and thermoelectric properties of Bi_2O_2Se with O and Se defects. Oxygen vacancies trap bands located inside the band gap of Bi_2O_2Se, and the compound becomes a conductor. These bands lead to drastic reduction in the Seebeck coefficient. When vacancies are filled by selenide atoms (selenide point defect), the materials return to be a semiconductor and the Seebeck coefficient increases. The increase of S is also found in the system with defects formed by the substitution of oxygen atoms into selenide sites (oxygen point defect) in the pristine compound. The power factor significantly increases during p-type doping compared with that during n-type doping for the selenide point defect. However, differences in the two doping cases are less distinguished for the oxygen point defect. Hence, the selenide point defect, Bi_2O_(2-δ)Se_(1+δ) with p-type doping, is an effective way to increase the power factor and eventually the thermoelectric efficiency of Bi_2O_2Se.