Giant Defect-Induced Effects on Nanoscale Charge Separation in Semiconductor Photocatalysts

Defects can markedly impact the performance of semiconductor-based photocatalysts, where the spatial separation of photogenerated charges is required for converting solar energy into fuels. However, understanding exactly how defects affect photogenerated charge separation at nanometer scale remains quite challenging. Here, using time- and space-resolved surface photovoltage approaches, we demonstrate that the distribution of surface photogenerated charges and the direction of photogenerated charge separation are determined by the defects distributed within a 100 nm surface region of a photocatalytic Cu₂O particle. This is enabled by the defect-induced charge separation process, arising from the trapping of electrons at the near-surface defect states and the accumulation of holes at the surface states. More importantly, the driving force for defect-induced charge separation is greater than 4.2 kV/cm and can be used to drive photocatalytic reactions. These findings highlight the importance of near-surface defect engineering in promoting photogenerated charge separation and manipulating surface photogenerated charges; further, they open up a powerful avenue for improving photocatalytic charge separation and solar energy conversion efficiency.