Phase evolution for oxidizing bismuth selenide.

The novel Bi 2 O 2 Se, produced by the oxidation of the layered Bi 2 Se 3 , 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 Bi 2 Se 3 to the monoclinic Bi 2 OSe 2 , and then to the tetragonal Bi 2 O 2 Se 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 Bi 2 Se 3 and O 2 and have a potential contribution to the application of optoelectronic devices. The intermediate Bi 2 OSe 2 with calculated band gap of 1.01 eV, may be a candidate for photovoltaic application in future.