Over the 3D ratio of ~60%, the intermediate-n (e.g., n=3-5), as well as the n=1 2D phases start to emerge, at the expense of the 3D-like HPs. This suggests that the formation of 3D-like HP phases are no longer to be favorable over this composition ratio. Essentially, this seems to be counterintuitive to the conventional perovskite chemistry, where, stoichiometrically, higher-n HP phases are deemed to be emerged when the 3D composition ratio becomes dominant in the system. In fact, analogous phase emergence features were observed in formamidinium (FA)-based quasi-2D HPs , hypothesizing that thermodynamically favorable δ-FAPbI3 phase can disturb the growth of 3D-like phases at such high 3D composition ratios. Considering this, the observed scenarios in this study can also be associated with the formation of thermodynamically favorable δ-CsPbI3 phase.