Anomalous Dependence of Photocarrier Recombination Time on the Polaron Density of TiO 2 (110).

Polarons play a crucial role in energy conversion, but the microscopic mechanism remains unclear since they are susceptible to local atomic structures. Here, by employing ab initio nonadiabatic dynamic simulations, we investigate electron-hole (e-h) nonradiative recombination at the rutile TiO 2 (110) surface with varied amounts of oxygen vacancies (V o ). The isolated V o facilitates e-h recombination through forming polarons compared to that in the defect-free surface. However, aggregated V o forming clusters induce an order-of-magnitude acceleration of polaron diffusion by enhancing phonon excitations, which blocks the defect-mediated recombination and thus prolongs the photocarrier lifetime. We find that photoelectrons are driven to migrate toward the top surface due to polaron formation. Our results show the many-body effects of defects and polaron effects on determining the overall recombination rate, which has been ignored in the Shockley-Read-Hall model. The findings explain the controversial experimental observations and suggest that engineering V o aggregation would instead improve photocatalysis efficiencies in polaronic materials.