Ultrafast Observation of Carrier Dynamics in TiO₂ Using Time Resolved X-ray Absorption Spectroscopy.

Understanding photo-excited carrier dynamics is essential for developing advanced materials for solar energy utilization. The behavior of photo-generated carriers plays a crucial role in driving chemical reactions on the catalyst surface.

In this study, we demonstrate the ability to directly probe the dynamics of photo-generated holes in TiO₂ using femtosecond time-resolved X-ray absorption spectroscopy with a soft X-ray free-electron laser at PAL-XFEL. Initially, electron or hole carriers are captured by acceptor or donor-type defects, such as metal or oxygen vacancies in their neutral states. These captured carriers subsequently recombine with oppositely charged polarons, leading to charged defect sites that are proposed to act as active sites for catalysis.

Our study provides critical insights into carrier dynamics in TiO₂, significantly advancing our understanding of photocatalytic processes and opening new avenues for energy-related applications. These findings underscore the importance of real-time, element-specific observations in unraveling the complexities of photocatalytic materials.