Polaron formation and transport in Bi₂WO₆ studied by DFT+U and hybrid PBE0 functional approaches

Bi₂WO₆ (BWO) is considered as a promising material for photocatalytic water splitting. Its unique layered structure leads the charge separation, and transport is different from other materials. However, the charge transport mechanisms in BWO are not well understood. In this work, we investigated polaron formation and transport in BWO using the DFT+U and hybrid PBE0 functional approaches. We found that the electron will form 2-dimensional (2D)-shaped polarons among W sites in the ab plane of BWO with approximately 55% polaron density state on the central W site. This type of polaron is similar to the electron polarons in WO₃. For other W-based materials, the electrons may also form a 2D-shaped polaron. We found that the W 6s orbital plays an important role in these 2D-shaped electron polarons. The calculated mobility of electron polarons in BWO was consistent with experimental findings. For the hole state, it could form a small hole polaron on the O site with O 2p in character. However, it will not form a polaron on the Bi site, which is quite different from BiVO₄. This study provides insight for understanding polaron formation and transport in materials with W and Bi ions. It also provides understanding regarding charge separation and transport for materials with layered structures.