Mixed Organic Cations Promote Ambient Light-Induced Formation of Metallic Lead in Lead Halide Perovskite Crystals

Abstract

One major concern toward the performance and stability of halide perovskite-based optoelectronic devices is the formation of metallic lead that promotes nonradiative recombination of charge carriers. The origin of metallic lead formation is being disputed whether it occurs during the perovskite synthesis or only after light, electron, or X-ray beam irradiation or thermal annealing. Here, we show that the quantity of metallic lead detected in perovskite crystals depends on the concentration and composition of the precursor solution. Through a controlled crystallization process, we grew black-colored mixed dimethylammonium (DMA)/methylammonium (MA) lead tribromide crystals. The black color is suggested to be due to the presence of small lead clusters. Despite the unexpected black coloring, the crystals show higher crystallinity and less defect density with respect to the standard yellow-colored DMA/MAPbBr 3 crystals, as indicated by X-ray rocking curve and dark current measurements, respectively. While the formation of metallic lead could still be induced by external factors, the precursor solution composition and concentration can facilitate the formation of metallic lead during the crystallization process. Our results indicate that additional research is required to fully understand the perovskite precursor solution chemistry.

Surface Engineering of Methylammonium Lead Bromide Perovskite Crystals for Enhanced X-ray Detection

“…The crystals were grown using solvent acidolysis crystallization (SAC), in which N -methylformamide (NMF) is used as both solvent and source of methylammonium (MA) cations. ,− The control MAPbBr 3 crystals (labeled as Control-1M), synthesized from a 1 M PbBr 2 solution in NMF and HBr without the use of any antisolvent, were found to be nonemissive under UV light (Figure a–b), which is expected from such bulk mm-sized crystals. On the other hand, the crystals developed through slow diffusion of an antisolvent (DCM) to a 0.2 M PbBr 2 solution in NMF and HBr (labeled as DCM-0.2M) resulted in the formation of crystals with bright green emission under UV light (Figure c–d).…”