Nickel oxide (NiOₓ) is a cornerstone hole transport material for inverted perovskite solar cells (PSCs), yet conventional sol–gel methods often suffer from thermal annealing-induced defects that impede charge extraction. In this work, we demonstrate a synergistic interface-engineering approach to enhance the chemical and electrical robustness of NiOₓ thin films. By integrating ethylenediamine (EDA) as a chelating agent with subsequent γ-ray irradiation, we effectively regulated the sol–gel kinetics and electronic properties of the NiOₓ layer. The EDA-mediated surface, characterized by abundant hydroxyl groups, facilitated the uniform anchoring of a MeO-2PACz self-assembled monolayer (SAM), optimizing both molecular orientation and energy-level alignment. Consequently, the dual-modified NiOₓ/SAM architecture yielded a high power conversion efficiency (PCE) of 24.06% and significantly improved device stability