The n-type and p-type conductivity mechanisms of the bulk BiOCl photocatalyst from hybrid density functional theory calculations

In this work, the n-type and p-type conductivity mechanisms of bulk BiOCl are systematically investigated using first-principles calculations. Under the O-rich growth conditions, BiOCl presents the intrinsic p-type conductivity, which primarily originates from the contributions of the antisite defects O-Cl. This is in excellent agreement with the observed p-type conductivity in BiOCl under high oxygen partial pressure or in oxygen-saturated solutions in experiments. While BiOCl displays the intrinsic n-type conductivity under the Bi-rich growth conditions, the vacancy defects V-Cl are responsible for the character. Nevertheless, the extrinsic means or effects could lead to the production and ionization of the O vacancies, which could contribute to the n-type conductivity in BiOCl. Therefore, the intrinsic n-type conductivity behavior reported in BiOCl in recent experiments is well explained. Under the Cl-rich growth conditions, the major donor defects V-Cl and the major acceptor defects V-Bi in BiOCl compensate each other, leading to an intrinsic insulator. However, it is shown that the usual unintentional H impurities H-Bi could form the p-type conductivity in BiOCl under Cl-rich growth conditions and enhance the p-type conductivity under O-rich growth conditions. This helps to understand the p-type conductivity behavior reported or mentioned in BiOCl in many experiments. At the same time, we found that Group II elements Ca and Sr are superior p-type doping elements for BiOCl under the Cl-rich and O-rich growth conditions. The defect physics in the bulk BiOCl photocatalyst is well understood. This work may inspire more magnificent studies on developing BiOCl-based photocatalysts.