and LiF*

Organometallic trihalide perovskites have shown to be remarkably efficient as a light absorbing layer in a solar cell, which has prompted a tremendous surge in research interests. Several of their environmental and long term operational instabilities preventing widespread commercialization, are still actively being investigated by the community. One of their more puzzling instabilities, is the influence of light exposure to the active perovskite layer. Previous reports have shown substantial chemical and structural degradation to the perovskite material as a result of exposure. In an effort to better understand the influence of light exposure on a full device, we investigated the impact light exposure had on the interface between CH₃NH₃PbI₃ and LiF with xray photoemission spectroscopy measurements. An interface with LiF was chosen, as LiF is chemically stable under most conditions and has commonly been used as an insulating buffer layer in OLEDs. While the chemical degradation was similar to previous reports, the binding energy shifts of the interface with LiF differed with the pure perovskite degradation. Surface morphology changes were also recorded with a scanning electron microscope.