High-quality NiO_x nanoparticles synthesized via low temperature chemical precipitation method for high-performance inverted perovskite photovoltaics

Dual hole transport layers consisting of NiO_x and self-assembled molecules are widely adopted in inverted perovskite solar cells, yet plagued by high impurity content, inefficient hole transport, low molecular coverage, weak interfacial binding, unstable buried interface and energy level mismatch. Herein, a low-temperature chemical precipitation strategy is developed to synthesize high-quality NiO_x nanoparticles as hole transport layers. Compared with the room-temperature route, the low-temperature prepared NiO_x films deliver an elevated Ni³⁺/Ni²⁺ ratio, reduced impurities, higher electrical conductivity and hole mobility. Moreover, this strategy improves molecular coverage, alleviates energy level mismatch, accelerates hole extraction and strengthens buried interface stability. The optimized cells achieve a certified power conversion efficiency of 27.1%, and the 14 cm² minimodule reaches an efficiency of 23.18%. The devices retain 91.5% efficiency after 2100 h of continuous operation, and 91.4% efficiency after 2000 h of damp-heat aging.