Next, we examined the effect of a larger bulky spacer having two phenyl rings. DPA renders completely different phase emergence features in quasi-2D HPs compared with other systems (Figure ). It should be noted that pure DPA2PbI4 cannot be crystallized unless a minute concentration of 3D CsPbI3 (at least 2 mol.%) is incorporated in the precursor state. With a small amount of 3D precursors, crystallization occurs, producing yellow-colored films exhibiting distinctive asymmetric PL spectra peaked at ~490 nm. Such an unconventional HP crystallization feature and PL behaviors are likely due to the steric hindrance of DPA caused by the proximity of the neighboring phenyl rings at the 2D HP surface .