In this group, we study the correlation between structure and properties in complex semiconductors on a micrometer to subnanometer scale. The modern, multinary compounds under investigation are used, for example, in thin film solar cells and numerous electronic and optoelectronic devices. A main focus of our work is the determination of the element-specific atomic-scale structure and its influence on important material properties. Furthermore, structural and compositional inhomogeneity in the nano- to micrometer range often plays a crucial role for the device performance. A comprehensive understanding of the correlation between preparation conditions, chemical composition and structure as well as electrical and optical properties is indispensable in order to utilize the potential of these material systems even more efficiently in the future. To that end, we apply different, typically synchrotron based X-ray techniques and various electron microscopy methods and we closely collaborate with a large number of national and international research groups.