Ruthenium Complex Optimized Contact Interfaces of NiOX Nanocrystals for Efficient and Stable Perovskite Solar Cells

Nickel oxide (NiO X ) is a desirable hole‐transporting material for perovskite solar cells owing to their merits of low‐cost, stable, and readily scalable. However, the NiO X |perovskite interface suffers from serious recombination and poor photostability because of the interfacial redox reactions. Herein, NiO X nanoparticles with tunable size have been synthesized at low temperatures by controlling the reactivity of the hydrolysis reaction. A self‐assembled monolayer composed of a ruthenium complex, i.e., C106, is then introduced to optimize the interfacial properties. The C106 molecule chemically bonds to NiO X via carboxyl acid group, which passivates the surface defects of NiO X and suppresses the negative redox reaction at the interface. The modification leads to an improvement in perovskite film morphology, crystallization, and band alignment. As a result, the efficiency of solar cells has been improved from 18.1% to 20.5%. More importantly, the modified solar cells retain >80% of their initial performance after continuous operation under 100 mW cm −2 irradiation for 800 h, which is much enhanced than the unmodified devices.