Improved Stability of Organometal Halide Perovskite Films and Solar Cells toward Humidity via Surface Passivation with Oleic Acid

Abstract

Organometal halide (OMH) perovskites are highly promising for photovoltaic (PV) and other applications. However, their instability toward environmental factors such as humidity presents a major challenge in their potential commercial use. In this study, we developed a method to modify the surface of CH3NH3PbI3 perovskite films by spin coating oleic acid (OA) to create a water resistant layer that results in enhanced stability and PV performance. The OA-surface passivated perovskites were studied using FT-IR spectroscopy, UV–vis absorption spectroscopy, and X-ray diffraction (XRD). The samples were aged in dark humid air at ∼76% relative humidity (RH) for 4 weeks. The surface passivated films showed minimal signs of decomposition, and the PV devices showed better performance than the unpassivated devices. A possible explanation is the carboxyl group (−COO–) of OA binds to surface Pb2+ and/or CH3NH3+ to both passivate these surface defect sites, resulting in the formation of a thin layer of OA with their hydrophobic tail away from the perovskite film surface that effectively prevents water molecules from reaching the perovskite.