Multi-modal X-ray microscopy is a key technique to correlate material properties and structure with high spatial resolution for various kinds of samples. Specifically, the spatial correlation of X-ray fluorescence (XRF, composition and topography), X-ray beam induced current (XBIC, electrical performance) and X-ray excited optical luminescence (XEOL, optical performance) is of highest interest for solar cell development.
We report on the establishment of a combined setup for temporally (TR) and spectrally-resolved (SR) XEOL that can be used in parallel with further modalities at the synchrotron source PETRA III.
We use this setup to investigate triple-cation mixed-halide perovskite (Cs_xMA_0.15FA_0.85−xPb(I_0.8,Br_0.2)₃) solar cells (PSCs) with varying Cs content. These PSCs exhibit spatially varying performance and are thus ideally probed by multi-modal X-ray microscopy. We validate earlier findings relating wrinkle structures in the absorber to the Cs content (XRF).  Our nanoscale characterization of the wrinkles unveils a decrease in Br content (XRF) in thicker absorber areas, corresponding to a segregation of I and Br. This leads to a narrowing of the bandgap (SR-XEOL) and is accompanied by an increased lifetime (TR-XEOL), which could either be due to defect passivation by Cs or a charge-carrier funnelling to the narrower bandgap.
Furthermore, we will present an outlook to multi-modal measurement schemes at upcoming 4th generation storage rings where the tradeoff between flux and coherence will be relaxed.