Bismuth chalcohalides and oxyhalides as optoelectronic materials

Several Tl and Pb based halides and chalcohalides have recently been discovered as promising optoelectronic materials [i.e., photovoltaic (PV) and gamma-ray detection materials]. Efficient carrier transport in these materials is attributed partly to the special chemistry of ns2 ions (e.g., Tl+, Pb2+, and Bi3+). Density functional calculations of electronic structure, dielectric properties, optical properties, and defect properties are performed on selected Bi3+ based chalcohalides and oxyhalides, i.e., BiSeBr, BiSI, BiSeI, and BiOBr. We propose different applications for these Bi compounds based on calculated properties, i.e., n-BiSeBr, p-BiSI, and p-BiSeI as PV materials, BiSeBr and BiSI as room-temperature radiation detection materials, and BiOBr as a p-type transparent conducting material. The strong screening and the small anion coordination numbers in Bi chalcohalides should lead to weak potentials for electron localization at anion vacancies. Defect calculations indeed show that the anion vacancies (Se and Br vacancies) in BiSeBr are shallow, which is beneficial to efficient electron transport.