Note that NMF analysis also identifies similar phase emergence behaviors at both the top and bottom surface of the BDA-based quasi-2D HPs (Figure , S10b and S11), again revealing the vertically homogenized phase distributions in this system. While this feature can benefit the optoelectronic performances when the films are employed in PV devices, however, an extremely low power conversion efficiency (PCE) of 0.39% is recorded (Figure ). Such a poor PV performance is likely attributed to considerable charge carrier loss through the abundant surface defects as well as the emergence of non-HP δ-CsPbI3 crystallites in the quasi-2D HP matrices (vide infra).