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

Abstract 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 PEA 2 MA 4 Pb 5 I 16 < n > = 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.