Mechanistic Insights into Ultrafast Charge Transfer between CsPbBr ₃ Nanocrystals and 8-Aminoquinoline via Surface and Diffusion Pathways

Perovskite nanocrystals (PNCs) have attracted significant attention for next-generation photovoltaic and optoelectronic applications owing to their outstanding light-harvesting and charge-transport properties. However, despite extensive research, the fundamental mechanisms governing charge-carrier separation and interfacial charge-transfer processes in PNC-based systems remain incompletely understood, particularly the role of surface-bound versus freely diffusing molecular acceptors. In this work, we address this knowledge gap by investigating the excited-state interactions between cesium lead bromide (CsPbBr 3 ) PNCs and 8-aminoquinoline (AQ), a molecule capable of strong surface attachment. FTIR analysis confirms the binding of AQ to the PNC surface, while photoluminescence (PL) studies reveal efficient quenching of CsPbBr 3 emission in the presence of AQ. Ultrafast femtosecond upconversion and transient absorption spectroscopy demonstrate rapid hole transfer from photoexcited PNCs to surface-bound AQ, whereas nanosecond PL measurements indicate an additional diffusion-controlled hole-transfer pathway involving free AQ molecules in solution. The quenching efficiency remains nearly constant (∼67%) at different excitation wavelengths, confirming the dominant contribution of surface-bound AQ in the ultrafast process. These findings provide the first direct evidence of dual-time scale hole-transfer dynamics between CsPbBr 3 PNCs and AQ, distinguishing ultrafast surface-mediated charge transfer from slower diffusion-controlled interactions. The study offers important insights into interfacial charge-separation mechanisms in perovskite nanocrystal systems and may aid the rational design of more efficient photovoltaic and optoelectronic devices.