Ultrafast Charge Carrier Dynamics in Layered CuO‐TiO ₂ Heterostructure via Time‐Resolved Soft X‐Ray Absorption Spectroscopy

ABSTRACT Understanding the ultrafast carrier dynamics at the p‐n heterojunctions is indispensable for designing efficient photocatalysts. In this work, we used element‐specific time‐resolved soft X‐ray absorption spectroscopy (tr‐XAS) to investigate the ultrafast carrier transfer dynamics in a layered CuO/TiO ₂ heterostructure. On monitoring the transient response at the oxygen K‐, Cu L ₃ ‐, and Ti L ₃ ‐edges, it revealed hole accumulation at the CuO valence band (VB) on the timescale of several nanoseconds, whereas the photoexcited electron undergoes several processes. We observed that soon after photoexcitation, the electrons from the TiO ₂ conduction band (CB) diffuses into the CuO CB within ∼150 ps. However, the diffused electrons drifted towards the TiO ₂ CB within ∼800 ps, as it is energetically aligned at lower position and exhibits large electron population. The electrons there stays for longer durations ∼3500 ps by getting trapped into the deep trap states. This spatial separation, driven by the internal electric field of the p‐n interface, significantly suppresses the electron‐hole recombination. Our findings demonstrate that a ∼2.8 nm CuO overlayer effectively stabilizes long‐lived charge carriers, providing a basis for the enhanced photocatalytic performance observed in these heterostructures.