Three-dimensional and multimodal X-ray microscopy reveals the impact of voids in CIGS solar cells

The formation of small voids in polycrystalline absorbers has been repeatedly reported, whether after device fabrication or degradation. Although it certainly increases risk of delamination and complicates deposition of additional top layers and cells, it is not clear whether or how detrimental it is for photovoltaic performance. In our study, using synchrotron imaging, we non-destructively probe local performance deficits attributable to voids and highlight the complex 3D nature of structural defects in high-efficiency thin-film CIGS solar cells. We find that, although possibly detrimental at a local level, voids only have a minor effect at the device level, given the abundance of voids and the high efficiency of the cell. Our quantification of the absolute electron densities at the nanoscale may enable the development of adequate comprehensive models simulating structural and electronic defects. In the full presentation, we will show high-resolution images and 3D renderings of nanostructures in CIGS and put them in the context of spatially resolved performance measurements. Furthermore, we will showcase recent developments in X-ray imaging and give an outlook to technical developments at new X-ray sources that will become available in the coming years and enable a further increase of sensitivity and spatial resolution.