Surface Termination of Solution-Processed CH₃NH₃PbI₃ Perovskite Film Examined using Electron Spectroscopies

The interfaces of a perovskite solar cell significantly influence the charge processes in the cell, which contributes to the device performance with direct implication for surface potential, electronic structure, and chemical reactivity. The properties of the interface are strongly affected by the surface termination. In this work, the combination of ultraviolet photoelectron spectroscopy (UPS) and metastable-atom electron spectroscopy is demonstrated, to examine the surface termination of a solution-processed CH₃NH₃PbI₃ perovskite film. The results show that the surface of the CH₃NH₃PbI₃ perovskite film is terminated with a layer consisting of CH₃NH₃ and I. The interface energy level alignment for both occupied and unoccupied levels between CH₃NH₃PbI₃ and C60 is also examined using UPS and low-energy inverse photoelectron spectroscopy. It turns out that an ideal energy level alignment is established for the electron collection and hole block at the perovskite and C60 interface.