Perovskite precursor solutions (PPS) with eight different phenylmethylammonium (also called benzylammonium) spacer contents were prepared. In the following, for the sake of clarity, we use the notation N-x for a PPS Ruddlesden-Popper stoichiometry of n=x. It is distinguished from the perovskite crystal phases found in layers with a n stoichiometry. We investigated N-1, N-2, N-3, N-5, N-6, N-9, N-30 and N-i (infinite) initial compositions. Upon annealing, visual inspections revealed two distinct stages in the films' color. Stage-1 was characterized by the initial color change (CC) from yellow-translucent or brown-translucent to orange or dark brown (Supplementary Video 1). The characteristic CC time decreased from 12 s to 4 s with increasing N-value. As shown in Supplementary Fig. , an increase in N-value resulted in a darker color of the film and a shorter duration of Stage-1. During the annealing process, the formation of various phases was always accompanied by a reduction in the amount of residual solvent in the system. The removal of solvent residues, primarily bound to the perovskite precursors, is a crucial step in the phase formation and growth of the MHP film. To track the S element contained in the DMSO solvent, we performed real-time GD-OES measurements on all eight types of MHP films upon the annealing and after the color change (Supplementary Note 1 and 2). This technique, thoroughly described in Refs , has been used here for the first time to investigate the layer formation of reduced-dimensional MHPs. A detailed data analysis description is provided in Supplementary Note 3. An important parameter is the differential solvent elimination speed between the upper layer and the lower layer. The speeds correspond to line slopes displayed in Fig. and Supplementary Fig. , whereas the differential speed has been quantified by calculating the Gap index (GI) as described in Supplementary Note 2. The results are reported in Fig. for the eight different systems. We observed that, for the high N values, the solvent elimination was relatively homogeneous, with low GI values. On the other hand, lower N samples exhibited a downward elimination with a higher elimination speed at the upper layer compared to the lower layer (Fig. and Supplementary Fig. ). The GI parameter was the highest for N-3 (see Fig. ). We show below that each phase has a fixed growth direction in the studied systems. The 2D phases grow downward, causing the solvent evaporation rate in the upper layer of the film to be faster than that in the lower layer. The N-3 system has the highest GI parameter (Fig. ) and then the highest differential solvent elimination speed between the upper layer and the lower layer. In N-2 system, where the molar ratio of 2D and 3D in the precursor solution is 1:1, we observed that the GI was + 43.3 % (Supplementary Table ). For higher N, the GI parameter progressively decreases and the solvent elimination became more homogeneous. However, because the quasi-2D and quasi-3D films are multiphase, the description of the solvent behavior is insufficient to inform us about the crystallization behavior and complementary experiments are required.