The structural changes occurring during the annealing process of perovskite films can lead to morphological changes, especially in Quasi-2D and Quasi-3D systems. Thereby, we used scanning electron microscopy (SEM) to examine the film morphology at two annealing times: CC and FA (CC: annealing at the sample color change; FA: fully annealed) (Supplementary Fig. ). By comparing the top-surface and cross-sectional morphology of MHP films at CC and FA, we discovered that the growth and transformation of various phases affected the overall morphology of the film. Fig. illustrates the morphology of the N-5 at CC. In addition to the typical 3D perovskite grain morphology (yellow dotted box), we also observed structures resembling long bars (black dotted box) at the film surface. Interestingly, this morphology disappears when the sample is fully annealed (FA in Fig. ). The Fig. cross-sectional SEM image depicts a three-dimensional shape of such an elongated platelet, exhibiting a preferential vertical alignment in the perovskite film. We also found that this morphology disappears with increasing annealing time (Fig. ). Therefore, we assume that this type of morphology exists only for a few tens of seconds after annealing. On this basis, we recorded the change in the morphology during annealing using cross-section SEM images and observed how the morphology of the elongated platelets disappeared during annealing (see