Layer Distortion\nEngineering for Spontaneous Charge\nSeparation in Two-Dimensional Perovskites

Charge separation in highly confined type-I two-dimensional\n(2D)\nperovskites with a single inorganic layer (<i>n</i> = 1)\nremains challenging due to their excessive exciton binding energy.\nHerein, we engineer the layer distortion within Ruddlesden–Popper\n(RP) type perovskites (<i>n</i> = 1) by tailoring the sizes\nof the cycloalkylamine ligands. The perovskite layers are more distorted\nand corrugated to accommodate the highly compact yet rigid cyclopropylammonium\nand cyclobutylammonium, facilitating the formation of Pb–Pb\nand I–I ionic dimers as self-localizing sites for charge carriers.\nConsequently, spontaneous electron–hole separation as well\nas a long-lived (>1 μs) intrinsic quantum confined Stark\neffect\n(QCSE) is achieved using the thresholdless optical pump and without\napplying any external electric field, yielding an unprecedent amount\nof the photoinduced bandgap energy lowering. This work opens up new\npossibilities of efficient charge separation in type-I 2D quantum\nwells for the photovoltaic and nonlinear optical modulation applications.