DOI: https://doi.org/10.29363/nanoge.emlem.2022.042
Publication date: 15th July 2022
In semiconductors, exciton or charge carrier diffusivity is typically described as an inherent material property. Here, we show that the transport of excitons, which are bound electron-hole pairs, in CsPbBr3 perovskite nanocrystals (NCs) depends markedly on how recently those NCs were occupied by a previous exciton. Using fluence- and repetition-rate-dependent transient photoluminescence microscopy (TPLM), we visualize the effect of excitation frequency on exciton transport in CsPbBr3 NC solids. Surprisingly, we observe a striking dependence of the apparent exciton diffusivity on excitation laser power that does not arise from nonlinear exciton-exciton interactions nor from thermal heating of the sample. Upon photoexcitation, NCs transition to a transient configuration exhibiting an order-of-magnitude faster exciton transport rate. The transient configuration persists for ~microseconds at room temperature, and does not depend on the identity of surface ligands or presence of an oxide shell, suggesting that it is an intrinsic response of the perovskite lattice to electronic excitation. The finding of a transient enhancement in excitonic coupling between NCs may help explain other extraordinary photophysical behaviors observed in CsPbBr3 NC arrays, such as superfluorescence. Additionally, faster exciton diffusivity under higher photoexcitation intensity is likely to provide practical insights for optoelectronic device engineering.
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