Light-Induced Phase Mixing as One Origin for the Degradation of Phase-Impure 2D Perovskite Solar Cells

Quasi-two-dimensional perovskites have emerged as promising photovoltaic materials due to their remarkable stability compared to conventional 3D perovskites; however, their stability still falls short of the requirements for practical applications. Therefore, understanding the origins of intrinsic instability in 2D perovskite solar cells is essential for promoting their widespread use in optoelectronic technologies. Here, we studied the degradation of solar cells based on two kinds of 2D perovskite phases, aligned mix phase and pure phase, and found under light aging, the aligned mix phases gradually reverted to stoichiometric phases, indicative of light-induced phase mixing. During the aging process, the morphology of the perovskite thin films deteriorated, accompanied by an increase in the number of bulk-phase defects. To mitigate this phase mixing behavior, we employed larger-volume ligands to prepare 2D perovskites. The perovskite devices based on (OA)2(FA)3Pb4I13 demonstrated remarkable stability, maintaining 95% of their initial PCE after 4000 h of maximum power point tracking under one-sun illumination, representing one of the most stable quasi-2D perovskite solar cells to date.