Resolving Nano-Morphologies: A Pathway to Cross-Grain Homogeneous Cation Distribution in Perovskites
Cation segregation in formamidinium-cesium (FA-Cs) mixed-cation perovskites remains a critical barrier to the long-term operational stability of perovskite solar cells (PSCs). While compositional and microstructural engineering has advanced power conversion efficiencies (PCEs), grain-to-grain cation inhomogeneity at the nanoscale persists, compromising device durability. This analysis examines recent work by Zhou's group, which establishes a direct correlation between cross-grain cation homogenization and the thermodynamics-driven morphologic grooving of as-formed grain boundaries (GBs). These grooves merge at triple junctions to form nanoscale groove traps (nano-GTs) that impede cation mixing. By pre-incorporating butylammonium acetate (BAAc), the average nano-GT depth was reduced from 15.3 nm to 4.4 nm, driven by enhanced heterointerface energy. High-resolution atomic force microscopy (AFM) confirmed shallower nano-GT geometries, while cathodoluminescence (CL) hyperspectral mapping revealed that pristine samples exhibit distinct CL emissions across grains due to FA-Cs inhomogeneity. In contrast, shallowed nano-GT films show no discernible CL emission variation among grains, indicating homogeneous cation distribution. These findings provide a quantitative morphological lever for suppressing phase segregation and enhancing the operational longevity of perovskite-based devices.