Phase evolution for oxidizing bismuth selenide

The novel Bi2O2Se, produced by the oxidation of the layered Bi2Se3, has been considered as one of the most promising candidates for the next-generation electronics owing to its high carrier mobility and air-stability. In this work, by using crystal structure prediction and first-principles calculations, we report the phase transformations from the hexagonal Bi2Se3 to the monoclinic Bi2OSe2, and then to the tetragonal Bi2O2Se with the gradual oxidization. Owing to the difference in electronegativity between selenium (Se) and oxygen (O), the oxidation process is accompanied by an increase in bond ionicity. Our results shed light on the phenomena occurring in the interaction between the precursors Bi2Se3 and O2 and have a potential contribution to the application of optoelectronic devices. The intermediate Bi2OSe2 with calculated band gap of 1.01 eV, may be a candidate for photovoltaic application in future.