In recent years hybrid organic-inorganic perovskites (HOIPs) have received significant research attention mainly because of their use as active layer in perovskite solar cells (PSC). In combination with the commonly used silicon (= tandem cells), they record to a power conversion efficiency of 29.5%. HOIPs can be prepared spanning the whole range of dimensionalities: 3D, 2D, 1D and 0D. This results in a class of hybrid materials with highly tunable compositions, structures and properties. After the rise of the 3D HOIPS for use in PSCs, the lower- dimensional 2D hybrids are currently receiving increased attention. These 2D HOIPs consist of an organic layer, sandwiched between inorganic layers (templates), which relates to their generally enhanced material stability compared to the 3D HOIPs and on the other hand to their much higher degree of compositional flexibility. In order to establish structure-property relationships and improve solar cell devices, especially used as flexible thin films, we need to elucidate the exact structures of these 2D HOIPs. However, crystallization of these systems shows structural diversity, depending on the crystallization methods, thin film deposition techniques, solvents, etc. used. Therefore, it is within the ambition of this project to unravel all details of the crystallization process and enable a deep understanding of the fundamental triggers of the growth mechanism acting on the formation of these 2D HOIPs.