We will perform in operando GIWAXS studies of the perovskite solar cells under illumination and voltage bias. We will track the structural changes such as development of lattice strain, halide phase segregation and changes in grain orientation. We will study mixed wide-bandgap and medium band-gap perovskite solar cells and investigate how organic additives (various organic molecules with diammonium functional groups) influence the performance and stability of the solar cells. By correlating the structural changes with degradation of optical and electronic properties, we will establish the relation between the structure and properties of the solar cells.