Temporal Evolution of Self-Assembled Lead Halide Perovskite Nanocrystal Superlattices: Effects on Photoluminescence and Energy Transfer

TL;DR

This study investigates how the reactivity and structural evolution of CsPbBr3 nanocrystal superlattices influence their photoluminescence properties, revealing effects that mimic superfluorescence and emphasizing the importance of reactivity in collective optoelectronic behavior.

Contribution

It demonstrates that nanocrystal reactivity within superlattices can cause spectral features similar to collective phenomena, challenging interpretations of such features as superfluorescence.

Findings

Superlattice contraction and nanocrystal coalescence occur over days under vacuum.

Low energy emission peaks and shortened lifetimes are observed at 4 K.

Reactivity-induced changes can mimic superfluorescence effects.

Abstract

Excitonic/electronic coupling and cooperative interactions in self-assembled lead halide perovskite nanocrystals were reported to give rise to a collective low energy emission peak with accelerated dynamics. Here we report that similar spectroscopic features could appear as a result of the nanocrystal reactivity within the self-assembled superlattices. This is demonstrated by using CsPbBr3 nanocrystal superlattices under room temperature and cryogenic micro-photoluminescence spectroscopy. It is shown that keeping such structures under vacuum, a gradual contraction of the superlattices and subsequent coalescence of the nanocrystals occurs over several days. As a result, a narrow, low energy emission peak is observed at 4 K with a concomitant shortening of the photoluminescence lifetime due to the energy transfer between nanocrystals. When exposed to air, self-assembled CsPbBr3 nanocrystals develop bulk-like CsPbBr3 particles on top of the superlattices. At 4 K, these particles produce a distribution of narrow, low energy emission peaks with short lifetimes and excitation fluence-dependent, oscillatory decays, resembling the features of superfluorescence. Overall, the reactivity of CsPbBr3 nanocrystals dramatically alters the emission of their assemblies, which should not be overlooked when studying collective optoelectronic properties nor confused with superfluorescence effects.