Controlled Aqueous Synthesis of 2D Hybrid Perovskites with Bright Room-Temperature Long-Lived Luminescence.

Recently, some organic-inorganic hybrid perovskites (OIHPs) have been reported to exhibit strong subgap broadband luminescence. While the origin of such luminescence has been proposed by several groups, a strategy to prepare OIHP with the desired subgap emission properties has remained elusive. Here, we report controlled synthesis of a broadband-emitting single-crystal 2D OIHP with an average quantum yield of >80 %. We demonstrate that the intensity of broadband emission can be tuned by controlling the excess iodine ion concentration during the synthesis in hydroiodic acid. We show that the emitters exhibit characteristics of localized defects such as limited mobility and saturation at high excitation power. Using density functional theory calculations, we show that bond-state iodine interstitials are responsible for the observed long-lived luminescence.