The inorganic hole transport layer of nickel oxide (NiOx) has shown highly efficient, low‐cost, and scalable in perovskite photovoltaics. However, redox reactions at the interface between NiOx and perovskites limit their commercialization. In this study, ABABr (4‐(2‐Aminoethyl) benzoic acid bromide) between the NiOx and different perovskite layers to address the issues has been introduced. How the ABABr interacts with NiOx and perovskites is experimentally and theoretically investigated. These results show that the ABABr molecule chemically reacts with the NiOx via electrostatic attraction on one side, whereas on the other side, it forms a strong hydrogen bond via the NH3+ group with perovskites layers, thus directly diminishing the redox reaction between the NiOx and perovskites layers and passivating the layer surfaces. Additionally, the ABABr interface modification leads to significant improvements in perovskite film morphology, crystallization, and band alignment. The perovskites solar cells (PSCs) based on an ABABr interface modification show power conversion efficiency (PCE) improvement by over 13% and maintain over 90% of its PCE after continuous operation at maximum power point for over 500 h. The work not only contributes to the development of novel interlayers for stable PSCs but also to the understanding of how to prevent interface redox reactions.

While there is promising achievement in terms of the power conversion efficiency (PCE) of perovskite solar cells (PSCs), long-term stability has been considered the main obstacle for their practical application. In this work, the authors demonstrate the small monomer 2-(dimethylamino) ethyl methacrylate (DMAEMA) with unsaturated carboxylic acid ester bond in the antisolvent for perovskite formation to improve the PCE and stability. The results show that DMAEMA is self-polymerized and uniformly distributed in the film, contributing to the improved crystallinity of the perovskites. Equally important, it is found that there are newly established interactions of Pb 2+ and DMAEMA, and iodine and ternary amine between DMAEMA and perovskites, which improves the uniformity of the lead (II) iodide vertical distribution along with the films and thus phase stability, as well as largely decreases defects density in the film. Overall, the inverted PSCs with DMAEMA exhibit a open-circuit voltage of 1.10 V, short-circuit current of 23.86 mA cm −2 , fill factor of 0.82, and finally PCE reaches 21.52%. Meanwhile, the PSC stability is significantly improved due to the inhibition of the formation of iodine, reduction of the uncoordinated Pb 2+ , and suppression of phase segregation.