Influence of intermolecular interactions on ion migration at 2D/3D perovskite interfaces

Passivating the surface defects of three-dimensional (3D) perovskite layers with two-dimensional (2D) perovskites is a critical strategy for achieving high efficiency and stability in perovskite solar cells. However, the dynamic evolution of 2D/3D interfaces under external stimuli such as thermal stress and longterm illumination significantly impacts device performance. In this study, we systematically investigate the role of intermolecular interactions in governing ion migration at 2D/3D interfaces by physically stacking three 2D perovskite, (BA)2PbI4 (BA=butylammonium), (PEA)2PbI4 (PEA=phenethylammonium), and (BDA)PbI4 (BDA=1,4-butane diammonium), with 3D perovskite-MAPbI3 (MA=methylammonium), followed by thermal annealing; and subsequent characterization was carried out using ultraviolet-visible (UV-Vis) absorption and femtosecond-transient absorption (fs-TA) spectra. Our findings reveal that small MA+ ions migrate from the 3D perovskite into the 2D perovskites, forming quasi-2D perovskites and introducing new decay pathways, while BA+ and PEA+ ions back-incorporate into the 3D lattice, causing a slight blue shift of 2–3 nm in exciton peaks. Notably, no significant ion migration is observed at the (BDA)PbI4/MAPbI3 interface due to strong hydrogen bonds, demonstrating superior robustness against ion movement. Further analysis indicates that the stability of 2D/3D interface is governed by intermolecular interactions, following the order: hydrogen bonds > π-π stacking > van der Waals forces. These findings highlight the pivotal role of molecular interactions in modulating ion migration at 2D/3D interfaces and provide a clear design principle for constructing stable 2D/3D heterojunctions by selecting diammonium cations with robust hydrogen bonds, offering key insights for the rational design of stable perovskite interfaces.