Lead halide perovskites (LHPs) have been developed into promising materials for next-generation energy-efficient LEDs and solar cells. The LHP LED efficiency has become 45.5%, and solar cell efficiency has become 25.5%. Nevertheless, defects, including halide vacancies, adversely affect the efficiencies and stabilities of these devices. Therefore, the characteristics of such defects are important for optimizing the current-to-photon and photon-to-current conversion efficiencies of LHP LEDs and solar cells. The electroluminescence (EL) helps us to understand the carrier recombination dynamics in an LHP single-crystal LED. We report EL spectral fluctuations, intensity variations, and blinking of emitting centers in LHP single microcrystals from time-and intensity-correlated EL and PL data. Single-particle EL spectra reveal stochastically switching carrier recombination centers at different heights or positions within a MAPbBr 3 microcrystal play a central role in the EL intensity, and blinking time. The ON-and OFF-time probability distributions of emitting centers in a crystal fit a truncated power law with an early ON-time cutoff, suggesting multiple charge recombination processes in blinking, such as the presence of multiple quantum dots in a crystal. The emitter-quencher correlated EL blinking in single microcrystals follows the charging−discharging (type-A) mechanism, known for strongly quantum-confined systems. Interestingly, the EL ON-time truncates, and the number of emitted photons increases by filling the halide vacancies, underscoring the importance of minimizing halide vacancies in LEDs.

Repeated absorption of emitted photons, also called photon recycling, in large crystals and thick films of perovskites leads to delayed photoluminescence (PL) and decrease of PL intensity. The role of distinct band gaps, which act as donors and acceptors of energy, and nonradiative energy transfer on such delayed, low intensity emission is yet to be rationalized. Here we report delayed emission by nonradiative energy transfer across a distribution of energy states in close‐packed crystallites of cesium lead bromide CsPbBr3, formamidinium lead bromide FAPbBr3, or the mixed halide FAPb(BrI)3 perovskite synthesized in the form of thick pellets by the piezochemical method. The PL lifetime of the bromide‐rich domain in the mixed halide pellet is considerably decreased when compared with a pure FAPbBr3 pellet. Here the domains with higher bromide composition act as the energy donor, whereas the iodide‐rich domains are the acceptors. Time‐resolved PL measurements of CsPbBr3, FAPbBr3, and the mixed halide FAPb(BrI)3 perovskite pellets help us to clarify the role of nonradiative energy transfer on photon recycling.

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The role of nonradiative energy transfer on photon recycling in perovskite solids has been clarified by preparing thick pellets of lead halide perovskites. Nonradiative energy transfer is detected in piezochemically synthesized perovskite pellets in which the distributed energy states are closely packed. The mixed bromide–iodide lead perovskite with distinct donor–acceptor states is also investigated to clarify the mechanism of photon recycling. More information can be found in the Communication by S. Ghimire, V. Biju et al. on page 2133.