Self-formed of 3D Structure on the Edges of 2D Ruddlesden-Popper Perovskites

The observation of low energy edge photoluminescence and its beneficial effect on the solar cell efficiency of RP perovskites have unleashed an intensive research effort to reveal its origin. While, a reliable and consistent explanation is still missing and the underlying material structure on the edges has still not been identified. Using 2D (BA)₂(MA)₂Pb₃Br₁₀ as an example, we show that 3D MAPbBr₃ is formed on the edge due to the loss of BA. This self-formed MAPbBr₃ can explain the reported edge emission, while the reported intriguing optoelectronic properties such as fast exciton trapping from the interior 2D perovskite, rapid exciton dissociation and long carrier lifetime can be understood via the self-formed 2D/3D lateral perovskite heterostructure. The 3D perovskite is identified by the emergence of XRD signature from freezer-milled nanometer-sized 2D perovskite, submicron infrared spectroscopy and its photoluminescence response to external hydrostatic pressure. The revelation of this edge emission mystery and the identification of a self-formed 2D/3D heterostructure provide a new approach for developing the new optoelectronic devices based on the 2D RP hybrid perovskites.