Delineation and Passivation of Grain‐Boundary Channels in Metal Halide Perovskite Thin Films for Solar Cells

Abstract A simple, generic method for delineating grain‐boundary (GB) channels in metal halide perovskite (MHP) thin films for scanning electron microscopy (SEM) observation is demonstrated, thereby enabling more accurate grain‐size measurements. This entails dipping the film in dichloromethane (DCM), followed by a moderate heat‐treatment, resulting in the in situ hydrocarbon functionalization of the film surface. More importantly, the hydrocarbons appear to congregate preferentially at GB‐channels, providing enhanced secondary‐electron contrast in the SEM. The hydrocarbons also provide extra protection to the vulnerable GB‐channels against environmental attack, resulting in improved environmental stability of DCM‐treated films. Also, the resulting solar cells show improved efficiency and operational stability.