The 2D GIWAXS patterns of the ThEA-based film majorly exhibit ring-shaped patterns, whereas the peaks of the principal 2D HPs (e.g., n=1 and 2 phases) are strong along the OOP direction (Figure ). These 2D HPs become predominant at the bottom, which agrees well with the vertical phase inhomogeneity seen in PL observations. Meanwhile, the emergence of weak Braggs spots along the Qz=~1.0 Å - 1 indicates that the 3D-like HP phases in this system are also vertically aligned. Moreover, strong emergences of δ-CsPbI3 and PbI2 crystallites corroborate that ThEA cannot bestow good phase stability of the resulting quasi-2D HPs. In the PEA-based film, the Braggs spots become more discrete, whereas the scattering rings are weakened (Figure ), suggesting more oriented growth of the crystallites in the matrix. According to the 1D scattering patterns, overall, similar phase emergence and vertical phase inhomogeneities are observed in the PEA-based system. A stark difference from ThEA counterpart is the absence of the δ-CsPbI3 and PbI2 crystallites. This further corroborates that PEA indeed offers good stability in the quasi-2D HP thin films.