Ab Initio Insights into Charge Localization in Bismuth Oxyhalides BiOX (X = F, Cl, Br, I)

Abstract

Developing efficient photocatalysts for clean energy generation is crucial to achieving net-zero emissions. To this end, we investigate the behavior of photoexcited charges in bismuth oxyhalides BiOX (X = F, Cl, Br, and I), a family of inexpensive and promising photocatalysts. To model the localization of excess electrons and holes, we use hybrid density functional theory PBE0(α). Our results indicate that electron polarons are unstable in these materials. Concurrently, we find that hole localization is favorable, and we identify two different possible configurations in which polarons are formed. One consists of two dimerized halogen atoms (VKcenter) and is preferentially formed in BiOBr and BiOI with binding energies that amount to -0.26 and -0.21 eV, respectively. The other corresponds to localization on a single Bi site and the surrounding oxygen and halogen atoms (BiXO). This form of polaron is favorable in BiOF and BiOCl with binding energies that amount to -0.35 and -0.23 eV, respectively. These findings highlight the behavior of photogenerated carriers and may open up avenues for future investigations on carrier transport in bismuth oxyhalides.