Recent years have witnessed a rapid development of all-inorganic halide perovskite in optoelectronic devices. Ultrathin 2D CsPbBr 3 nanosheets (NSs)with large lateral dimensions have demonstrated exceptional photophysical properties because of their analogous exciton electronic structure to quantum wells. Despite the incredible progress on device performance, the photophysics and carrier transportation parameters of quantum-confined CsPbBr 3 NSs are lacking, and the fundamental understanding of the exciton dissociation mechanism is far less developed. Here, a ligands rearrangement mechanism is proposed to explain why annealed NS films have an increased charge transfer rate and a decreased exciton binding energy and lifetime, prompting tunneling as a dominant way of exciton dissociation to separate photogenerated excitons between neighboring NSs. This facile but efficient method provides a new insight to manipulate perovskite nanocrystals coupling. Moreover, ultrathin 2D CsPbBr 3 NS film is demonstrated to have a enhanced absorption cross section and high carrier mobility of 77.9 cm 2 V −1 s −1 , contributing to its high responsivity of 0.53 A W −1 . The photodetector has a long-term stability up to three months, which are responsible for reliable perovskite-based device performance.

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