The BA-based film exhibits a rough and crumbled surface morphology with many voids (diameters of 100-300 nm), suggesting that considerable defects are likely present in the matrix. Particularly, the voids can be attributed to the low boiling point of BA (78 o C), which can facilitate its vaporization upon film fabrication. In the BDAbased film, rod-shaped structures emerge. It is found that these features are exactly overlapped with the emission signals in the corresponding 445 nm-filtered CL map, which is confirmed as δ-CsPbI3 (Figure ) . Note that appreciable 445-nm signals are also observed in BA-based quasi-2D HP film, although the corresponding crystallites are not found in the SEM image. This suggests that the δ-CsPbI3 crystallites are intercalated within the HP matrices, as a result of the deformation from the 3D-like phases . In contrast, the rod-shaped δ-CsPbI3 crystallites at the BDA-HP film surface corroborate that both HP and non-HP phases are concurrently constructed upon the crystallization process, rather than deformation . We hypothesize that, the slow crystallization dynamics in this system, attributed to the strong chemical interaction between BDA and inorganic precursors, causes the separated growth of the quasi-2D HPs and non-HP phases, rather than promoting the higher-n HP growths (vide infra). Also, a large number of voids (smaller than the BA counterpart; <100 nm) are observed. Given the high boiling point of BDA (~158 o C), those voids can be attributed to the both slower crystallization kinetics of DJ-type 2D HPs and thermodynamic preference of the δ-CsPbI3 formation at the low processing temperature . We map the CL signals at ~680-700 nm for each film (Figure ). These wavelengths respectively correspond to the CL peak of the 3D-like HPs (the average and local CL spectra collected from each film are shown in Figure ). In both cases, stronger CL signals of 3D-like phases are observed in the surface voids. Similar CL intensity enhancements were observed from the grain boundaries in 3D HP films, attributed to the higher free carrier concentrations promoting radiative recombination . Given such voids are associated with the evaporation of the spacer, it is hypothesized that large amounts of molecular spacers are congregated at the local sites. In turn, this can manifest a higher density of the coordinated spacers on the HP surface, thereby passivating the surface defects and accelerating radiative recombination .