Mapping structure heterogeneities and visualizing moisture degradation of perovskite films with nano-focus WAXS

Extensive attention has focused on the structure optimization of perovskites, whereas rare research has mapped the structure heterogeneity within mixed hybrid perovskite films. Overlooked aspects include material and structure variations as a function of depth. These depth-dependent local structure heterogeneities dictate their long-term stabilities and efficiencies. Here, we use a nano-focused wide-angle X-ray scattering method for the mapping of film heterogeneities over several micrometers across lateral and vertical directions. The relative variations of characteristic perovskite peak positions show that the top film region bears the tensile strain. Through a texture orientation map of the perovskite (100) peak, we find that the perovskite grains deposited by sequential spray-coating grow along the vertical direction. Moreover, we investigate the moisture-induced degradation products in the perovskite film, and the underlying mechanism for its structure-dependent degradation. The moisture degradation along the lateral direction primarily initiates at the perovskite-air interface and grain boundaries. The tensile strain on the top surface has a profound influence on the moisture degradation. Understanding the correlation between moisture degradation and structural features of perovskite films is essential to improve their stability. Here, the authors apply nano-focused wide-angle X-ray scattering to map the heterogeneities over several micrometers across lateral and vertical directions.

Automated summary

In this study, nano-focused wide-angle X-ray scattering was used to map the heterogeneities of perovskite films. The results show that the top film region bears tensile strain and perovskite grains deposited by sequential spray-coating grow along the vertical direction. Moreover, moisture degradation primarily occurs at the perovskite-air interface and grain boundaries, and the tensile strain on the top surface has a profound influence on the moisture degradation.