Reversible Light-Induced Enhancement of Photoluminescence Lifetime and Intensity in Perovskite-Phase CsPbI₃ Nanocrystals

Abstract

Light-induced changes in photophysical and electronic properties in metal halide perovskites can affect their performance in photovoltaic devices, light-emitting diodes, and other applications. Here we reveal that light induces a slow, reversible enhancement in photoluminescence (PL) lifetime and intensity in films of perovskite-phase CsPbI3 nanocrystals. When films of CsPbI3 nanocrystals stored in air are photoexcited, their PL lifetime and intensity increase by as much as a factor of 5 over the course of 20–30 min. Several hours later, without additional light excitation, the initial PL lifetime and intensity return. Placing the films under vacuum or nitrogen for several minutes was also found to increase the PL lifetime and intensity. We propose a model of slow, humidity- and light-sensitive surface states in perovskite-phase CsPbI3 nanocrystals.

A-Site Cation Dependence of Self-Healing in Polycrystalline APbI3 Perovskite Films

“…The fluorescence lifetime of the nonbrightened regions was ∼0.6 ns (average of 4 spots), whereas, for brightened areas, it was ∼0.9 ns (average of 5 spots), depending on the power density. This increase in the lifetime of emission from a photobrightened area is consistent with a reduction in nonradiative recombination. , …”

“…This increase in the lifetime of emission from a photobrightened area is consistent with a reduction in nonradiative recombination. 28,29 While for CsPI photobrightening occurred within the exposed ROIs, in some but not all FAPI films, we found PL enhancement at the periphery of ROIs, at higher power densities ((1.1−1.5) × 10 5 W/cm 2 ; Figure S9 gives an example for photobrightening in a FAPI film). This finding indicates that photodamage to, and SH dynamics in, the film has both a temporal and a spatial component.…”

“…This effect was attributed to surface states caused by humidity, passivated by illumination; apparently, this photobrightening was not reversible under an inert atmosphere. 28 Fluorescence lifetime imaging on the brightened areas, using a ps pulsed laser, showed lifetimes in the ns range (Figure S8b). The fluorescence lifetime of the nonbrightened regions was ∼0.6 ns (average of 4 spots), whereas, for brightened areas, it was ∼0.9 ns (average of 5 spots), depending on the power density.…”

“…γ-CsPI nanocrystal films were previously found to undergo reversible photobrightening if exposed to light in ambient air. This effect was attributed to surface states caused by humidity, passivated by illumination; apparently, this photobrightening was not reversible under an inert atmosphere …”

Experimental Verification of the Accuracy of Oxygen-Varying Correlated Fluorescence for Determining the Quenching Constant KSV

“…Theoretically, the Stern–Volmer equation , is utilized to express the relationship between phosphorescence quenching and oxygen content, which is as follows I normalp 0 I normalp = τ normalp 0 τ normalp = 1 + K normalS normalV [ O 2 ] where I p0 and I p and τ p0 and τ p represent the phosphorescence intensity and lifetime in the absence and presence of oxygen, respectively …”