A simple “cast-capping” method is adopted to prepare single-crystal perovskites of methyl ammonium lead bromide (CH3NH3PbBr3). By capping a CH3NH3PbBr3 solution casted on one substrate with another substrate such as glass, mica, and distributed Bragg reflector (DBR), the slow evaporation of solvent enables large-size cubic crystals to grow between the two substrates. Under optical pumping, edge-emitting lasing is observed based on Fabry–Pérot resonation between parallel side facets of a strip-shaped crystal typically with a lateral cavity length of a few tens of μm. On the other hand, vertical-cavity surface-emitting lasing (VCSEL) is obtained from a planar crystal grown between two DBRs with a cavity thickness of a few μm. Simultaneous detection of those edge- and surface-emissions reveals that the threshold excitation fluence of VCSEL is higher than that of the edge-emitting lasing due to thickness gradient in the planar crystal.

In this study, electroluminescence from single crystals of CH 3 NH 3 PbBr 3 perovskite is explored. The cast capping method was applied to fabricate simple devices with an ITO/CH 3 NH 3 PbBr 3 /ITO structure. The devices showed a low operation voltage of 2 V and a pure green luminescence with full width at half maximum of >20 nm. However, the emission occurring at the crystal edges demonstrated blinking with a subsecond time interval, which is similar to the previously reported photoluminescence behavior of nanocrystal perovskites. This electroluminescence blinking may provide new insight into the recombination processes depending on the carrier traps and defects of emission layers in perovskite light-emitting devices.

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Microcapillaries enable us to simply prepare crystalline perovskites in a microcavity. A precursor solution of methyl ammonium lead bromide (CH3NH3PbBr3) is injected by capillary action into quartz microcapillaries with an inner diameter (ϕ) of 2–40 μm. After drying at 70 °C in the atmosphere, cylindrical crystals are precipitated to fill up the inner cavity of the microcapillary. Under optical pumping, whispering gallery mode lasing depending on ϕ is observed. With reducing ϕ, the mode number and the lasing threshold fluence are found to be decreased. This suggests that the stimulated emission can be enhanced by cavity quantum electrodynamics in CH3NH3PbBr3 crystals which are densely confined in the microcavity. Consequently, the microcapillary with ϕ = 2 μm realizes single-mode lasing at a threshold fluence of 4.7 μJ/cm2.

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