Understanding the Structural Dynamics of 2D/3D Perovskite Interfaces

The incorporation of 2D perovskite capping layers has become common practice in high-performance lead halide perovskite solar cells to passivate 3D perovskite surface defects. However, recent work has shown these 2D/3D interfaces to be highly dynamic, undergoing structural transformation when subjected to thermal stress or illumination. Here, we study the structural dynamics of a series of commonly used alkylammonium-based Ruddlesden-Popper (RP) and Dion-Jacobson (DJ) phase 2D perovskites deposited on formamidinium lead iodide. By monitoring the grazing-incidence wide-angle x-ray scattering and photoluminescence of the 2D/3D perovskite heterostructures aged at 100°C or under 1 sun illumination, we observe that the 2D perovskite structures transform to progressively larger inorganic layer thickness (denoted by layer number n), eventually approaching a steady-state condition with only the 3D perovskite (n=∞) remaining. This transformation slows by a factor of two when increasing the size of the RP-forming ligand from butylammonium to dodecylammonium. Furthermore, substituting the RP-forming dodecylammonium with DJ-forming 1,12-dodecanediammonium of similar size, decelerates the structural transformation by a factor of 10. These findings suggest that the use of DJ 2D perovskite capping layers could be a promising pathway to form stable 2D/3D heterostructures.