The complex nature of Quasi-2D and Quasi-3D systems, which contain multiple 2D and 3Dd phases, led to a lack of systematic studies on the changes in their internal structure during annealing. Fig. and Supplementary Fig. depict the alterations in all phases followed by in situ GIWAXS, in both the upper layer and the whole layer of the studied films during the complete annealing time of 10 minutes. A general observation is that only N-2, N-3, N-5, and N-6 systems contain more than a single distinct phase. These four systems exhibit successive phases representing different perovskites. The analysis of the N-2 system in Figs. and shows that the phases appear in the 3D, n=2 and n=1 order with increasing annealing time. This phase succession is in full agreement with the formation energy of each structure, which we determined by DFT calculations (Supplementary Fig. ).