Insights into the Cation Migration Kinetics across 2D/3D Perovskite Interfaces and Strategy for Its Prevention

Incorporating a 2D perovskite layer on top of a 3D perovskite is an effective approach to enhance the long-term stability of 3D perovskite-based optoelectronic devices. However, cation migration across the interface of 2D and 3D perovskites, particularly under light or heat exposure, can lead to interfacial reconstructions. We investigated the cation migration kinetics across the interface of 2D BA2PbBr4 and 3D MAPbBr3 by physical pairing. We monitored changes in both perovskite layers by unpairing them to understand the migration of cations from one layer to the other. The 2D BA2PbBr4 film showed comparatively more changes than the 3D MAPbBr3 layer, which is due to the faster migration of smaller MA+ cation toward the BA2PbBr4 film, while the larger BA+ cation migrates at a slower rate toward the MAPbBr3 film. The activation energies of MA+ and BA+ cation migrations were found to be 63 and 138 kJ mol–1, respectively. Migration of the MA+ cation transformed the 2D BA2PbBr4 (n = 1) film into the higher dimensional quasi-2D perovskites (n = 2 and 3), with a higher "n" more at the surface. We also proposed and demonstrated a strategy to prevent cation migration by introducing the ultrathin ALD alumina layer between 2D and 3D perovskites.