摘要： The interfaces between perovskite and charge transport layers greatly impact the device efficiency and stability of perovskite solar cells (PSCs). Inserting an ultrathin wide bandgap layer between perovskite and hole transport layers (HTL) has recently been shown as an effective strategy to enhance device performance. Herein, a small amount of organic halide salt, N,N’-dimethylethylene-1,2-diammonium iodide, is used to create 2D-3D heterojunctions on MAPbI3 thin film surfaces by facile solution processing. The formation of ultrathin wide bandgap 2D perovskite layer on top of 3D MAPbI3 changes the morphological and photophysical properties of perovskite thin films, effectively reduces the surface defects, and suppresses the charge recombination in the interfaces between perovskite and HTL. As a result, a power conversion efficiency of ~ 20.2%, with an open circuit voltage of 1.14 V, a short-circuit current density of 22.57 mA cm-2, and a fill factor of 0.78, is achieved for PSCs with enhanced stability.