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

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.