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Improved understanding of the origins of instability during photovoltaic operation of perovskite solar cell materials must be established to overcome barriers to commercialization. In this study, we analyze the microscopic mechanisms of degradation in high-performing methylammonium free (FA0.9Cs0.1PbI3) perovskite solar cells (PSC) over 600 hours of operation under stressors inherent to PV operation, including heat, illumination, and a load while excluding atmospheric effects by testing in a water-and oxygen-free atmosphere. While the PSCs exhibit reasonable thermal stability, they show considerable performance loss under constant illumination or stable power output. Synchrotron-based nanoprobe X-ray fluorescence and X-ray beam induced current (XRF/XBIC) measurements reveal segregation of current-blocking Cs-rich phases during stress testing. The decrease in performance correlates with the resulting number density of the Cs-rich clusters, which varies by stress condition. These findings unveil cation-dependent instability in FA0.9Cs0.1PbI3 perovskites and provide a framework for understanding the energy landscape in alloy perovskites to guide the engineering of long-lived halide perovskite devices.

Compositional engineering related to the organic and inorganic cations (A-site) in halide perovskites solar cells has helped improve efficiency and long-term durability. However, this compositional complexity can lead to phase segregation that weakens the optoelectronic performance. Here, we show the halide distribution and cation distribution by means of synchrotron-based nanoprobe x-ray fluorescence. We find that the halide distribution homogenizes upon the addition of CsI and RbI precursors. The halide homogenization coincides with long-lived charge carrier decays. Additionally, we observe Rb-rich areas that phase segregate within the film and the Rb aggregates are identified to be recombination active using X-ray and E-beam induced current microscopy.

The poor stability of halide perovskites creates a barrier for common e-beam based microscopies. Thus, carefully optimized e-beam characterization conditions are needed before any meaningful measurement can be taken. In this study, we present a range of e-beam operating conditions for characterizing perovskite materials with minimal electronic damage by monitoring plan-view electron beam induced current (EBIC) of functional solar cell devices. We see a minimum of beam induced damage in plan-view operation the range of 7.5 to 9.5 kV at low currents (

In this study, we use nanoprobe X-ray diffraction to measure structural variations in thin halide perovskite single crystals including mosaicity, tilt and strain. Using X-ray diffraction at 100-nm spatial resolution offers high sensitivity to structural variations within thin film materials. Here, we examine the crystal structural changes under X-ray irradiation toward understanding in detail the determining factors in this process including chemistry of materials, dose, and dose rate.

Hybrid perovskite materials are promising for application as the active layers in solar cells due to their excellent optoelectronic properties. Improved understanding of the origins of hysteresis in perovskite materials must be established to overcome barriers to commercialization. In this study, we use a lateral device geometry to bias a methylammonium lead bromide thin film single crystal. Upon biasing, the halide concentration varies laterally within the crystal, as observed by means of nondestructive synchrotron-based nanoprobe X-ray fluorescence (Nano-XRF). The direct observation of a partially reversible bromine re-distribution under bias is revealed experimentally. The origins of device hysteresis and switchable effects can be partially explained by the local elemental information available from Nano-XRF.

Quasi-2D perovskite photovoltaics have been shown to have better stability than their 3D counterparts but the effects of the A-site cation on charge collection have not been fully clarified in these systems. In this study, the nanoscale carrier collection properties within quasi-2D bromide based lead perovskites (n=3 and 40) are found to be uncorrelated with local variations in halide stoichiometry, in contrast to the 3D perovskite. The local elemental distribution is quantified by means of synchrotron-based nanoprobe X-ray fluorescence (Nano-XRF), while the local carrier collection is simultaneous collected via X-ray beam induced current (XBIC).

Spatial heterogeneities in the chemical makeup of thin film photovoltaic devices are pivotal in determining device efficiency. In this study, the presence of chlorine is identified in perovskite films synthesized with Cl-containing precursors by means of nanoprobe X-ray fluorescence (Nano-XRF). Additionally, a spatial variation in the Cl incorporation is observed within a given film, and the standard deviation of Cl: I ratio across the film is large. Using Nano-XRF, the Cl incorporation in methylammonium lead iodide perovskite films can be manipulated by precursor stoichiometry ratio.