Spatially resolved fluorescence of caesium lead halide perovskite supercrystals reveals quasi-atomic behavior of nanocrystals

TL;DR

This study combines spatially resolved fluorescence and X-ray nanodiffraction to investigate surface defects in caesium lead halide perovskite supercrystals, revealing quasi-atomic behavior and emphasizing strain minimization for optimal optical properties.

Contribution

It introduces a combined experimental and modeling approach to link surface defects with optical properties in perovskite supercrystals, highlighting the quasi-atomic nature of nanocrystals.

Findings

Surface defects cause fluorescence blueshift and shorter lifetimes.

Structural coherence loss and strain are key factors affecting optical properties.

Minimizing strain is crucial for improving perovskite supercrystal performance.

Abstract

We correlate spatially resolved fluorescence (-lifetime) measurements with X-ray nanodiffraction to reveal surface defects in supercrystals of self-assembled caesium lead halide perovskite nanocrystals and study their effect on the fluorescence properties. Upon comparison with density functional modelling, we show that a loss in structural coherence, an increasing atomic misalignment between adjacent nanocrystals, and growing compressive strain near the surface of the supercrystal are responsible for the observed fluorescence blueshift and decreased fluorescence lifetimes. Such surface defect-related optical properties extend the frequently assumed analogy between atoms and nanocrystals as so-called quasi-atoms. Our results emphasize the importance of minimizing strain during the self-assembly of perovskite nanocrystals into supercrystals for lighting application such as superfluorescent emitters.