Hot Carrier Trapping in Light-Soaked Mixed Phase CsPbI3 Perovskite Nanocrystals

Abstract

Red-emitting CsPbI₃ 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.