Molecular interactions are crucial to improving the efficiency and stability of perovskite solar cells, yet current solution-based approaches relying on molecular incorporation or surface passivation show inherent limitations in separately controlling these interactions. Here we reveal an intrinsic interfacial interaction that arises from simple contact between individually crystallized two-dimensional and three-dimensional perovskites without mixing or permanent bonding. We define this contact-triggered cationic interaction (CCI), which reversibly constrains molecular degrees of freedom, suppresses phase transitions, enhances carrier lifetimes and induces a unique recrystallization of the three-dimensional framework. This CCI-driven recrystallization produces refined FAPbI3 with improved cation homogeneity, reduced lattice disorder and superior optoelectronic properties. Devices using CCI-driven FAPbI3 achieve 26.25% efficiency (25.61% certified) and retain a projected operational lifetime exceeding 20,000 h. Our findings provide the first quantitative evidence that intrinsic interfacial cationic interactions can directly influence perovskite material quality and device performance. Solution processing of 2D/3D perovskite structures for solar cells offers limited control over layer formation. Lee et al. propose a dry approach, bringing the 2D and 3D perovskite layers into physical contact, to enhance the quality of the perovskite film.