In layered hybrid perovskites, such as (BA)2PbI4 (BA=C4H9NH3), electrons and holes are considered to be confined in atomically thin two dimensional (2D) Pb–I inorganic layers. These inorganic layers are electronically isolated from each other in the third dimension by the insulating organic layers. Herein we report our experimental findings that suggest the presence of electronic interaction between the inorganic layers in some parts of the single crystals. The extent of this interaction is reversibly tuned by intercalation of organic and inorganic molecules in the layered perovskite single crystals. Consequently, optical absorption and emission properties switch reversibly with intercalation. Furthermore, increasing the distance between inorganic layers by increasing the length of the organic spacer cations systematically decreases these electronic interactions. This finding that the parts of the layered hybrid perovskites are not strictly electronically 2D is critical for understanding the electronic, optical, and optoelectronic properties of these technologically important materials.

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=0.1-3 μm ) 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. 4 μm) 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.

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 methylammonium lead bromide (MAPbBr 3 ) 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 (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.

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Abrupt fluorescence intermittency or blinking is long recognized to be characteristic of single nano-emitters. Extended quantum-confined nanostructures also undergo spatially heterogeneous blinking;h owever,t here is no such precedent in dimensionally unconfined (bulk) materials. Herein, we report multi-level blinking of entire individual organo-lead bromide perovskitemicrocrystals (volume = 0.1-3 mm 3 )u nder ambient conditions.E xtremely high spatiotemporal correlation (> 0.9) in intracrystal emission intensity fluctuations signifies effective communication amongst photogenerated carriers at distal locations (up to ca. 4 mm) within each crystal. Fused polycrystalline grains also exhibit this intriguing phenomenon, whichi sr ationalized by correlated and efficient migration of carriers to af ew transient nonradiative traps,t he nature and population of whichd etermine blinking propensity.O bservation of spatiotemporally correlated emission intermittency in bulk semiconductor crystals opens the possibility of designing novel devices involving longrange (mesoscopic) electronic communication.Fluorescence intermittencyo rb linking, which refers to temporally random discrete jumps in intensity between bright and dark levels,has been considered as one of the main pieces of evidence for the detection of single nano-sized quantum emitters. [1][2][3][4][5][6][7][8] Apart from single molecules,b linking is commonly observed in various individual quantum-confined systems such as semiconductor nanocrystals (NCs), in which excitons/charge carriers are spatially restricted in more than one dimension. [4][5][6][7][8][9][10][11][12][13] In NCs,photoluminescence (PL) blinking is attributed to intermittent Auger ionization-recombination processes leading to charging-discharging of NCs or longlived carrier trapping in surface (defect) states. [4,5,14,15] However,P Li ntermittencyi ss eldom observed beyond the nanoscale (approaching bulk), as temporally uncorrelated intensity fluctuations from various emitters average out over the ensemble and contribution of surface states in radiative recombination becomes less significant compared to that of free carriers in the bulk. [7] Even for 1D-or 2D-confined extended nanostructures, blinking beyond the diffraction limit (ca. 250 nm) is uncommon, and such PL intermittencyi ss patially heterogeneous, that is,s patiotemporally uncorrelated. [9,16] There is ar are example of spatially concerted PL intensity fluctuations in an extended quantum-confined system; [10] asmall proportion (1-2%)o fe ntire single CdSe quantum wires were found to exhibit correlated multilevel blinking, attributed to delocalized 1D excitons.w hich allow efficient long-range carrier migration. More recently,i ndividual stacked-monolayers of transition metal dichalcogenides (MoSe 2 /WS 2 )were reported to undergo temporally anti-correlated blinking arising from mobile 2D excitons,w hich experience sporadic interlayer charge transport. [17] Owing to their exceptional carrier diffusion lengths and diffusivities, [18,19] or...