Stress-Regulated Crystallization on Mesoporous Nickel Oxide Enables High-Efficiency and Stable Inverted Perovskite...

Nickel oxide (NiO_x) is one of the most widely employed hole transport layers (HTLs) in inverted perovskite solar cells (PSCs) due to its low-temperature processability, compatibility with scalable fabrication, and favorable energy-level alignment. Since 2015, extensive efforts have been devoted to enhancing the optoelectronic properties of NiO_x; however, most studies have predominantly focused on planar NiO_x (pNiO_x) films. In this study, we fabricate a mesoporous nickel oxide (mNiO_x) HTL via high-temperature calcination, using nickel nitrate hexahydrate (Ni(NO₃)₂·6H₂O) as the nickel precursor, Pluronic P123 and a small amount of polyvinylpyrrolidone (PVP) as structure-directing templates. The resulting mesoporous framework modulates the perovskite crystallization kinetics, enhances the buried interface, improves the crystallization quality, reduces the defect density, and shifts the interfacial stress state from tensile to compressive. Consequently, both the open-circuit voltage (V_OC) and fill factor (FF) of the devices are significantly enhanced. The PSCs based on the mNiO_x HTL achieve a power conversion efficiency (PCE) of 23.19%, along with markedly improved operation and storage stability.