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Abstract Correlative X‐ray microscopy, including synchrotron X‐ray diffraction and fluorescence, is leveraged to understand the local role of europium as a B‐site additive in CsPbBr₃perovskite crystals. Europium addition reduces microstrain in the perovskite, despite the fact that the degree of europium incorporation into the perovskite varies locally, with a maximum loading over twice the nominal stoichiometry. The presence of europium improves photoluminescence yield and bandwidth, while shifting the emission to bluer wavelengths. Finally, europium‐containing crystals have greatly improved X‐ray hardness. The findings show promise for europium as an additive in perovskite optoelectronic devices. 

Abstract X‐ray microscopy can provide unique chemical, electronic, and structural insights into perovskite materials and devices leveraging bright, tunable synchrotron X‐ray sources. Over the last decade, fundamental understanding of halide perovskites and their impressive performance in optoelectronic devices has been furthered by rigorous research regarding their structural and chemical properties. Herein, studies of perovskites are reviewed that have used X‐ray imaging, spectroscopy, and scattering microscopies that have proven valuable tools toward understanding the role of defects, impurities, and processing on perovskite material properties and device performance. Together these microscopic investigations have augmented the understanding of the internal workings of perovskites and have helped to steer the perovskite community toward promising directions. In many ways, X‐ray microscopy of perovskites is still in its infancy, which leaves many exciting paths unexplored including new ptychographic, multimodal, in situ, and operando experiments. To explore possibilities, pioneering X‐ray microscopy along these lines is briefly highlighted from other semiconductor systems including silicon, CdTe, GaAs, CuIn_xGa_1−xSe₂, and organic photovoltaics. An overview is provided on the progress made in utilizing X‐ray microscopy for perovskites and present opportunities and challenges for future work. 

Phase stability and the optoelectronic performance of the metastable CsPbI₃host can be improved with triple-halide alloying, without excessive Br addition which widens the gap beyond that ideal for tandem-photovoltaics. 

We present a design strategy for fabricating ultrastable phase-pure films of formamidinium lead iodide (FAPbI₃) by lattice templating using specific two-dimensional (2D) perovskites with FA as the cage cation. When a pure FAPbI₃precursor solution is brought in contact with the 2D perovskite, the black phase forms preferentially at 100°C, much lower than the standard FAPbI₃annealing temperature of 150°C. X-ray diffraction and optical spectroscopy suggest that the resulting FAPbI₃film compresses slightly to acquire the (011) interplanar distances of the 2D perovskite seed. The 2D-templated bulk FAPbI₃films exhibited an efficiency of 24.1% in a p-i-n architecture with 0.5–square centimeter active area and an exceptional durability, retaining 97% of their initial efficiency after 1000 hours under 85°C and maximum power point tracking. 

The light-emitting diodes (LEDs) used in indoor testing of perovskite solar cells do not expose them to the levels of ultraviolet (UV) radiation that they would receive in actual outdoor use. We report degradation mechanisms of p-i-n–structured perovskite solar cells under unfiltered sunlight and with LEDs. Weak chemical bonding between perovskites and polymer hole-transporting materials (HTMs) and transparent conducting oxides (TCOs) dominate the accelerated A-site cation migration, rather than direct degradation of HTMs. An aromatic phosphonic acid, [2-(9-ethyl-9H-carbazol-3-yl)ethyl]phosphonic acid (EtCz3EPA), enhanced bonding at the perovskite/HTM/TCO region with a phosphonic acid group bonded to TCOs and a nitrogen group interacting with lead in perovskites. A hybrid HTM of EtCz3EPA with strong hole-extraction polymers retained high efficiency and improved the UV stability of perovskite devices, and a champion perovskite minimodule—independently measured by the Perovskite PV Accelerator for Commercializing Technologies (PACT) center—retained operational efficiency of >16% after 29 weeks of outdoor testing. 

Abstract Understanding the optoelectronic properties of optically active materials at the nanoscale often proves challenging due to the diffraction-limited resolution of visible light probes and the dose sensitivity of many optically active materials to high-energy electron probes. In this study, we demonstrate correlative synchrotron-based scanning x-ray excited optical luminescence (XEOL) and x-ray fluorescence (XRF) to simultaneously probe local composition and optoelectronic properties of halide perovskite thin films of interest for photovoltaic and optoelectronic devices. We find that perovskite XEOL stability, emission redshifting, and peak broadening under hard x-ray irradiation correlates with trends seen in photoluminescence measurements under continuous visible light laser irradiation. The XEOL stability is sufficient under the intense x-ray probe irradiation to permit proof-of-concept correlative mapping. Typical synchrotron XRF and nano-diffraction measurements use acquisition times 10–100 x shorter than the 5-second acquisition employed for XEOL scans in this study, suggesting that improving luminescence detection should allow correlative XEOL measurements to be performed successfully with minimal material degradation. Analysis of the XEOL emission from the quartz substrate beneath the perovskite reveals its promise for use as a real-time in-situ x-ray dosimeter, which could provide quantitative metrics for future optimization of XEOL data collection for perovskites and other beam-sensitive materials. Overall, the data suggest that XEOL represents a promising route towards improved resolution in the characterization of nanoscale heterogeneities and defects in optically active materials that may be implemented into x-ray nanoprobes to complement existing x-ray modalities.