Hot Carrier Trapping in Light‐Soaked Mixed Phase CsPbI ₃ Perovskite Nanocrystals

Abstract Red‐emitting CsPbI ₃ perovskite nanocrystals (r‐PNCs) are considered promising for device applications due to their low bandgap. However, their practical use is hindered by significant photoluminescence (PL) intermittency and light‐induced phase transitions. Specifically, the stable and bright α‐phase of r‐PNCs quickly converts into weakly emissive mixed‐phase (δ and γ) within hours under UV irradiation. In the absence of light, r‐PNCs synthesized using an advanced method have been shown to maintain their α‐phase and brightness for over 20 days. This study explores the PL intermittency of r‐PNCs to better understand the carrier dynamics and the nature of trap states in both the α‐phase and mixed phases. These results indicate that r‐PNCs, despite their apparent phase stability, undergo rapid phase deformation during a blinking experiment, as evidenced by the decrease in the average ON state intensity of their PL trajectories and the change in XRD patterns. Fluorescence‐lifetime‐intensity‐distribution (FLID) mapping from blinking studies, combined with fluorescence lifetime correlation spectroscopy (FLCS), reveals that freshly prepared α‐phase r‐PNCs exhibit blinking behavior primarily governed by short‐lived trap states near the band edge. These dynamic trap states function as multiple non‐radiative recombination centers (MRCs). In contrast, light‐soaked mixed‐phase r‐PNCs develop long‐lived deep trap states, leading to dispersive blinking predominantly caused by hot carrier (HC) recombination.