Imaging and performance of CIGS thin film modules

With demonstrated efficiencies exceeding 20 % on a laboratory scale CIGS has advanced to the leading thin film PV technology. A major challenge is the transfer of such efficiencies to a module level and the demonstration of a high production yield. Imaging techniques such as thermography and electroluminescence can detect and identify local defects and inhomogeneities which limit the module performance and production yield. This contribution discusses imaging techniques (lock-in thermography, electroluminescence and photoluminescence) and their correlation to local electrical properties of highly efficient CIGS thin film modules which were produced in a non vacuum inline process. It will be shown that the benefit of imaging is not restricted to the detection of local shunt defects but can be extended, especially by the combination of complementary techniques, to the identification of regions with increased recombination, the detection of current inhomogeneities and to variations of material properties across the module surface. The interpretation of such images will be supported by correlation of imaging data with local measurements of the solar cell parameters, by a mapping of the electrical potential distribution across the module and by an assessment of the global module performance. Furthermore, 2D-network simulation will be applied in order to understand the impact of local inhomogeneities on the performance of an integrated module and on local parameters which are responsible for the appearance of thermography and luminescence images. Regarding the origin of such inhomogeneities structural and compositional material analysis and technology considerations will add to the understanding of performance limitations. It will be concluded that these imaging techniques are valuable and fast means not only for the quality control in a production line but also for the optimization of the module performance during a technology development.