The energy crisis and environmental pollution are attracting increasing attention, which made many countries implement a series of preferential policies for renewable energy. Among them, solar photovoltaic technology, which can convert solar light into electrical energy, is one of the most feasible methods for renewable energy. It not only improves environmental problems but also reduces dependence on fossil fuels. In recent years, perovskite solar cells has reviewed promising potential in solar photovoltaics owing to low process energy consumption, large-scale production, low cost, simple fabrication process, light weight, flexibility, etc. Polyhedral oligomeric silsesquioxane (POSS) possessing a hollow-cage or semi-cage structure is a new type of organic-inorganic hybrid nanoparticles. POSS combines the advantages of inorganic components and organic components to become one of the most important materials. When POSS is well dispersed in the polymer matrix, it can effectively improve the thermal, mechanical, magnetic, acoustic, and surface properties of the polymer. In this study, the POSS was spin-coated as a ultra-thin passivation layer to optimize a nickel-oxide hole layer, which made perovskite solar cells feature high open circuit voltage. Experimental results showed that Coating an appropriate POSS amount to form an ultra-thin passivation layer could effectively suppress the surface defects of perovskite layers, reduce the recombination of the electron and hole, and increase the short-circuit current. As a result, the power conversion efficiency increased from 13.30 to 15.58%, enhanced by 17%.