By using NMF analysis, the phase emergence behaviors at the bottom surface of the films are also examined (Figure ). As observed from composition-dependent PL spectra (Figure ), the RP-type quasi-2D HP systems exhibit the dominance of the low-n (n=1 and 2) 2D phases across the entire compositional range. These 2D HPs have larger bandgaps than those of 3D-like counterpart, manifesting energetic barriers between the underlying charge transport layer and 3D-like HP photoactive layer. Such energetic landscape, in turn, can impede efficient charge transport across the vertical direction, and consequently, curtail PV performances. Indeed, those quasi-2D HP films exhibit low PV performances (Figure , detailed device fabrication and characterizations in Experimental Section); here, an optimal 3D composition ratio of 60%, where the exclusive emergence of 3D-like phases is expected to be most probable, was employed. These observations suggest that mitigation of vertical phase inhomogeneities in the quasi-2D HPs is vital for demonstrating efficient PV devices.