Kesterites are used as absorbers in thin film solar cells. The interest in this material class is triggered by its low cost and abundant raw materials. However, their wide spread use is still hampered by a rather large loss in open circuit voltage compered to the ideal case. This is due to a strong tailing in the electronic structure. This tailing is caused by some disorder in the material, which is currently not understood. In this project we will use state-of-the-art atomic scale analysis methods to understand the correlation between nanoscale composition and the electronic structure.