Anomalous Dependence of Photocarrier Recombination Time on the Polaron Density of TiO₂(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.