Suppressing interfacial defect formation derived from in-situ-generated polyethylenimine-based 2D perovskites to boost the efficiency and stability NiOx-based inverted planar perovskite solar cells

Recently, NiO x -based inverted planar perovskite solar cells (PSCs) have achieved great progress. However, the lattice mismatch between NiO x hole-transport layers (HTLs) and perovskite active layers will result in interfacial defect formation, which severely influences device efficiency and stability. In this work, this is alleviated by coating of polyethylenimine cations (PEI•HI) on the surface of NiO x HTLs. The introduction of PEI•HI can not only effectively passivate the surface defects of NiO x films, but also induce the in-situ-generation of polyethylenimine (PEI)-based two-dimensional (2D) perovskite interlayers between NiO x and CH 3 NH 3 PbI 3 (MAPbI 3 ). Such PEI-based 2D perovskite interlayer can dramatically mitigate the lattice mismatch between NiO x and perovskites to suppress the interfacial defects formations and promote the high-quality crystal nucleation and growth of above perovskite films. Meanwhile, it is demonstrated that the molecular weights of PEI act the pivotal part in controlling the nucleation quality of perovskites. When employing PEI with molecular weight of 10,000 (PEI-1000), the high-crystalline perovskite film with large-sized grains and reduced interfacial defects is obtained and the champion PSC delivers a power conversion efficiency (PCE) of 19.23% with weak hysteresis effect and improved reproducibility and stability. Our work provides a promising approach to improve the lattice match between NiO x and perovskites for high-performance NiO x -based inverted planar PSCs.