Red-Shifted Photoluminescence from Crystal Edges Due to Carrier Redistribution and Reabsorption in Lead Triiodide Perovskites

Photoluminescence (PL) of CH3NH3PbI3 perovskites depends strongly on sample preparation, atmosphere, crystal size, and so forth. However, the origin of these dependencies is always misunderstood because of the co-works of many different factors. Herein, we prepared hexagonal-shaped single crystals with tens of micrometers in size and observed a red-shifted PL emission (800-830 nm) mainly from the crystal edges besides the usual band-to-band transition (760 nm) from the central regions. Also, significantly different time-resolved dynamics and excitation power dependencies were observed. To summarize, we conclude that the red-shifted component comes from the depth of the crystal, where monomolecular recombination occurs involving photogenerated charges and unintentional doped charges, while the normal PL is emitted by bimolecular recombination from the surface layers. These results showed the significance of pure optical effects in perovskite crystals and would promote detailed understanding of the charge dynamics and recombination in perovskite crystalline materials of different geometries and sizes.