Spatially Correlated Blinking of Perovskite Micro-crystals: Deciphering Effective Modes of Communication between Distal Photoexcited Carriers

Recent observations on spatially correlated photoluminescence (PL) intermittency (blinking or flickering) of bulk perovskite crystals have invoked considerable interest regarding their origins, as the ensemble averaging effect should result in heterogeneous intensity fluctuations over micron length scales. This intriguing phenomenon can only be explained by considering (i) photogeneration of few transient nonradiative traps which act as highly efficient quenchers for photoexcited charge carriers and (ii) long-range communication (or correlation) between a large number of spatially segregated (∼microns) charge carriers photogenerated simultaneously. In light of spatially synchronous blinking in systems with a length scale beyond diffusion parameters in microcrystalline thin films, we investigated the modes of excitation energy migration which augment intracrystal communication. Here, we used spectrally resolved wide-field epi-fluorescence microscopy with optional confocal (local) excitation to probe excited energy migration modes. We identified the waveguide effect and its assistance to produce secondary excitons through photon recycling in MAPbBr 3 microcrystals (MCs). Upon formation of nonradiative trap/s within the excitation domain, these secondary modes of carrier migration help in collective quenching of photogenerated carriers and redistribution of emission throughout the MC. This report discusses a method to investigate excitation migration in spatially extended systems and provides insights into the carrier communication process in bulk perovskites, which results in the PL blinking of entire individual MCs.