Flat and island-like features are distinctively observed in the DPA-based quasi-2D HP films (Figure ). Interestingly, no appreciable CL signal associated with δ-CsPbI3 is observed (Figure ), attributed to the outstanding phase stabilizing effect of DPA. The 3D-like HP phases exhibit CL peaked at the longer wavelength of 705 nm (Figure ) than that of the others, which almost replicates the emission of bulk CsPbI3 . This indicates DPA manifests the formation of thicker 3D-like HPs at the top surface. The steric hindrance between the neighboring DPA phenyl rings can restrict the complete surface coverage of the spacers on the HP lattice. This scenario can impede the termination of crystallization as 2D HP phases, thereby promoting the formation of thicker HP lattices. Note that some immature crystallites, without offering flat and island-like structures, are observed. Local CL spectra reveal that these structures exhibit blueshifted CL (~10nm) peaks (Crimson-colored curve, Figure ), indicating the formation of quasi-2D HPs thinner than those at the foremost top surface. This suggests that DPA cations are more abundant along the depth of the film, which can make more dimension-confined HP lattices.