Direct Observation of Crystal Engineering in Perovskite Solar Cells in a Moisture-Free Environment Using Conductive Atomic Force Microscopy and Friction Force Microscopy

The origin of the increased efficiency of perovskite solar cells by controlling environmental humidity was investigated using conductive atomic force microscopy (C-AFM) and friction force microscopy (FFM). The perovskite thin films fabricated in a humidity-free environment exhibited better crystallinity and a lower number of trap sites than the films fabricated in a high-humidity environment. Through in-depth analysis using C-AFM and FFM, we found that there was a locally decrystallized area in the perovskite structure fabricated in a high-humidity environment. By suppressing the local decrystallization in a humidity-free environment, the power conversion efficiency was increased by about 122%. This was mainly attributed to the increase in current density as the elimination of the locally decrystallized area increases the effective active area. From this perspective, mapping the local current and friction force using C-AFM and FFM could be new techniques for visualizing the effect of crystal engineering of perovskite solar cells in a humidity-free environment.