This work reports a dynamic self-passivation mechanism in high-quality FAPbI3 single crystals, originating from trap-state saturation under high excitation fluence and investigated using near-surface sensitive transient reflectance (TR) spectroscopy. Application of the inverse Hilbert transformation (iHT) to the TR signals enables high-sensitivity probing of carrier dynamics in the near-surface region, effectively suppressing contributions from the bulk. The experimental results indicate that an initial blue shift of the bandgap is primarily attributed to band filling effects from high-density photogenerated carriers. As pump fluence increases, the lifetimes of Auger (τ2) and defect-mediated (τ3) recombination first shorten and then show distinct anomalous elongation. This transition suggests that a high concentration of photogenerated carriers can transiently occupy surface deep-level trap states, thereby effectively suppressing nonradiative recombination channels. This dynamic trap-state passivation mechanism elucidates the enhanced carrier persistence in FAPbI3 under strong illumination, offering insights into its intrinsic interfacial behavior and providing a basis for optimizing the performance of related optoelectronic devices.
Pan et al. (Fri,) studied this question.