The appearance and growth of various perovskite phases observed by in situ GIWAXS analysis for the first 30 seconds of thermal annealing are presented in Figs. . It is found that the phases that appear during the initial annealing and their number vary for the different systems, notably due to the distinct formation energies of various structures (Supplementary Fig. ). The N-1 sample exhibits a pure n=1 phase while for N-9, N-30 and N-i, only the 3Dd phase is found. Table summarizes the MHP phases present for the various PPS compositions and their growth direction determined from in situ GIWAXS results.