Dipole orientation-induced interfacial energy level alignment difference in 2D perovskite passivated 3D perovskite by in situ investigation

Abstract

Interface passivation has been widely used in perovskite solar cell studies with multiple beneficial effects. Among them, energy level alignment is frequently mentioned but is mostly studied by ex situ measurement, which is unable to reveal subtle changes at the interface. In this study, we in situ investigated the interfacial energy alignment of MAPbI₃ passivated by two ammonium salts with long alkyl chains (butylammonium iodide and butane-1,4-diammonium iodide, BAI and BDAI). Both molecules formed a 0.11 eV interface dipole, but in opposite directions. The BAI deposition created an additional downward band bending on the BAI side, making it ideal for electron extraction. The BDAI deposition created an additional 0.12 eV valence band maximum (VBM) drop, imposing a barrier for hole transfer. Such non-optimum alignment could partially explain the lower device performance with BDAI passivation. Our results highlight the importance of in situ studies and reveal unseen details in the electronic structure at the passivation interface.