The BA-based film exhibits strong Bragg spots aligned along the Qz=~1.0 and ~2.0 Å -1 . This is a representative signature for the vertically aligned 3D HP lattice, which has been observed from various quasi-2D HP systems . That is, BA promotes the growth of vertically aligned 3D-like HP phases. Figure shows the corresponding 1D scattering profiles of the BA-based quasi-2D HP film along the out-of-plane (OOP) and in-plane (IP) directions, respectively. In addition to the 3D CsPbI3 lattice, scattering modes of n=1 and 2 2D HPs are observed. These peaks become stronger with increasing the angle of the X-ray beam, particularly along the OOP direction, indicating that these face-on stacked 2D HP phases become dominant towards the bottom surface. Meanwhile, appreciable peaks of δ-CsPbI3 and PbI2 are observed. These phases are produced as a result of the deformation of quasi-2D HP , indicating its poor stability in agreement with the emission behavior.