Photoluminescence Flickering of Micron-Sized Crystals of Methylammonium Lead Bromide: Effect of Ambience and Light Exposure

Recent reports on temporal photoluminescence (PL) intensity fluctuations (blinking) within localized domains of organo-metal lead halide (hybrid) perovskite microcrystals have invoked considerable interest to understand their origins. Using PL microscopy, we have investigated the effect of atmospheric constituents and photoillumination on spatially extended intensity fluctuations in rnethylammonium lead bromide (MAPbBr(3)) perovskite materials, explicitly for micrometer (ca. 1-2 mu m)-sized crystals. Increase in the relative humidity of the ambience results in progressive reduction in the PL intensity, and beyond a threshold value, individual microcrystalline grains exhibit multistate PL intermittency (flickering), which is characteristically different from quasi two-state blinking observed in nanocrystals. Such flickering disappears upon removal of moisture, accompanied by considerable enhancement of the overall PL efficiency. We hypothesize that initiation of moisture-induced degradation marked by the lowering of PL intensity correlates with the appearance of PL flickering, and such processes further accelerate in the presence of oxygen as opposed to an inert (nitrogen) environment. We find that the intrinsic defects not only increase the threshold level of ambient moisture needed to initiate flickering but also modulate the nature of PL intermittency. Our results therefore establish a strong correlation between initiation of material degradation and PL flickering of hybrid perovskite microcrystals, induced by transient defects formed via interaction with the ambience

Fluorescence Blinking Beyond Nanoconfinement: Spatially Synchronous Intermittency of Entire Perovskite Microcrystals

Abrupt fluorescence intermittency or blinking is long recognized to be characteristic of single nano-emitters. Extended quantum-confined nanostructures also undergo spatially heterogeneous blinking; however, there is no such precedent in dimensionally unconfined (bulk) materials. Herein, we report multi-level blinking of entire individual organo-lead bromide perovskite microcrystals (volume=0.1-3m(3)) under ambient conditions. Extremely high spatiotemporal correlation (>0.9) in intracrystal emission intensity fluctuations signifies effective communication amongst photogenerated carriers at distal locations (up to ca. 4m) within each crystal. Fused polycrystalline grains also exhibit this intriguing phenomenon, which is rationalized by correlated and efficient migration of carriers to a few transient nonradiative traps, the nature and population of which determine blinking propensity. Observation of spatiotemporally correlated emission intermittency in bulk semiconductor crystals opens the possibility of designing novel devices involving long-range (mesoscopic) electronic communication

Photoluminescence Flickering of Micron-Sized Crystals of Methylammonium Lead Bromide: Effect of Ambience and Light Exposure

Recent reports on temporal photoluminescence (PL) intensity fluctuations (<i>blinking</i>) within localized domains of organo-metal lead halide (hybrid) perovskite microcrystals have invoked considerable interest to understand their origins. Using PL microscopy, we have investigated the effect of atmospheric constituents and photoillumination on spatially extended intensity fluctuations in methylammonium lead bromide (MAPbBr₃) perovskite materials, explicitly for micrometer (ca. 1–2 μm)-sized crystals. Increase in the relative humidity of the ambience results in progressive reduction in the PL intensity, and beyond a threshold value, individual microcrystalline grains exhibit multistate PL intermittency (<i>flickering</i>), which is characteristically different from quasi two-state blinking observed in nanocrystals. Such flickering disappears upon removal of moisture, accompanied by considerable enhancement of the overall PL efficiency. We hypothesize that initiation of moisture-induced degradation marked by the lowering of PL intensity correlates with the appearance of PL flickering, and such processes further accelerate in the presence of oxygen as opposed to an inert (nitrogen) environment. We find that the intrinsic defects not only increase the threshold level of ambient moisture needed to initiate flickering but also modulate the nature of PL intermittency. Our results therefore establish a strong correlation between initiation of material degradation and PL flickering of hybrid perovskite microcrystals, induced by transient defects formed via interaction with the ambience