Defect-Induced Spin Splitting Extends Charge Carrier Lifetimes in Anatase TiO₂

Experiments have demonstrated that defects can introduce spin polarization and prolong the charge carrier lifetimes of photocatalysts, while the underlying mechanism remains unclear. Using time-dependent density functional theory and nonadiabatic molecular dynamics, our study reveals that the O vacancy in anatase TiO₂ almost does not cause evident electronic spin polarization while it creates a deep trap state within the band gap, functioning as an efficient charge recombination center. Charges are rapidly trapped within a few hundred femtoseconds, leading to fast electron-hole recombination. In contrast, the Ti vacancy induces pronounced spin polarization through the asymmetric splitting of spin electronic structures near the Fermi level. This creates net magnetic moments while activating spin-flip transitions, thereby prolonging charge carrier lifetimes by orders of magnitude compared to that of V_O systems. Our simulations reveal the microscopic effects of the vacancy-defect-induced spin polarization on the charge and spin dynamics, offering valuable insights for optimizing the performance of photocatalysts.