Evolution of Defects, Morphology, and Strain during FAMAPbI3 Perovskite Vacuum Deposition: Insights from In Situ Photoluminescence and X-ray Scattering.

At present, the power conversion efficiency of single-junction perovskite-based solar cells reaches over 26%. The further efficiency increase of perovskite-based optoelectronic devices is limited mainly by defects, causing the nonradiative recombination of charge carriers. To improve efficiency and ensure reproducible fabrication of high-quality layers, it is crucial to understand the perovskite nucleation and growth mechanism along with associated process control to reduce the defect density. In this study, we investigate the growth kinetics of a promising narrow bandgap perovskite, formamidinium methylammonium lead iodide (FAMAPbI3), for high-performance single-junction solar cells. The temporal evolution of structural and optoelectronic properties during FAMAPbI3 vacuum codeposition was inspected in real time by grazing-incidence wide-angle X-ray scattering and photoluminescence. Such a combination of analytical techniques unravels the evolution of intrinsic defect density and layer morphology correlated with lattice strain from the early stages of the perovskite deposition.

Probing the composition dependence of residual stress distribution in tungsten-titanium nanocrystalline thin films.

Nanocrystalline alloy thin films offer a variety of attractive properties, such as high hardness, strength and wear resistance. A disadvantage is the large residual stresses that result from their fabrication by deposition, and subsequent susceptibility to defects. Here, we use experimental and modelling methods to understand the impact of minority element concentration on residual stresses that emerge after deposition in a tungsten-titanium film with different titanium concentrations. We perform local residual stress measurements using micro-cantilever samples and employ machine learning for data extraction and stress prediction. The results are correlated with accompanying microstructure and elemental analysis as well as atomistic modelling. We discuss how titanium enrichment significantly affects the stress stored in the nanocrystalline thin film. These findings may be useful for designing stable nanocrystalline thin films.