Multimodal imaging of thin-film solar cells has been demonstrated at hard X-ray nanoprobes: simultaneously assessing X-ray beam induced current and X-ray fluorescence, lateral variations in the electrical performance and the distribution of absorber and trace elements can be correlated. Here, we complement the suite of modalities with scanning X-ray diffraction and map the crystallographic structure of Cu(In,Ga)Se2(CIGS) at the nanoscale: in the quaternary compound semiconductor, lattice strain and structural defects induced by tetragonal lattice distortions, steep vertical In/Ga gradients, and lateral inhomogeneities pose a great challenge. Investigating a series of solar cells with varying In/Ga ratio, we probed for the first time a statistically significant number of nearly 500 CIGS grains in the bulk layer of operational cells. Overall, we assessed the entirety of the Cu(In,Ga)Se2 Materials Science Tetrahedron—thanks to, first, extraordinary sensitivity with K-edge excitation allowing to correlate the lateral Cd and In/Ga distribution, local performance, and lattice spacing, second, detection of voids, some filled with CdS, in the CIGS layer, and third, performance-relevant findings from a crystallographic analysis of grain orientation and boundaries. Beyond further optimization of Cu(In,Ga)Se2 photovoltaic cells toward the detailed balance limit of solar-cell conversion efficiency, the developed methodology paves the way to extract a maximum of information from correlative hard X-ray nanoscopy at diffraction-limited storage rings.
Pyrlik et al. (Wed,) studied this question.