Efficient and Stable Quasi‐2D Ruddlesden–Popper Perovskite Solar Cells by Tailoring Crystal Orientation and Passivating Surface Defects

Solar cells (PSCs) with quasi‐2D Ruddlesden–Popper perovskites (RPP) exhibit greater environmental stability than 3D perovskites; however, the low power conversion efficiency (PCE) caused by anisotropic crystal orientations and defect sites in the bulk RPP materials limit future commercialization. Herein, a simple post–treatment is reported for the top surfaces of RPP thin films (RPP composition of PEA2MA4Pb5I16 = 5) in which zwitterionic n‐tert‐butyl‐α‐phenylnitrone (PBN) is used as the passivation material. The PBN molecules passivate the surface and grain boundary defects in the RPP and simultaneously induce vertical direction crystal orientations of the RPPs, which lead to efficient charge transport in the RPP photoactive materials. With this surface engineering methodology, the optimized devices exhibit a remarkably enhanced PCE of 20.05% as compared with the devices without PBN (≈17.53%) and excellent long‐term operational stability with 88% retention of the initial PCE under continuous 1‐sun irradiation for over 1000 h. The proposed passivation strategy provides new insights into the development of efficient and stable RPP‐based PSCs. A simple solution‐processable passivator is introduced on the top surface of low‐dimensional 2D perovskites. This passivator induces a vertical crystal orientation and simultaneously passivates the defects on the perovskites, leading to efficient charge transport with reduced recombination loss in the photoactive materials. The champion device exhibits a power conversion efficiency of 20.05% with negligible hysteresis and superior operational stability.