“…Afterward, the solution aging effect on the perovskite film crystallization was examined with a primary focus on (PEA) 2 SnI 4 , since it is the most widely explored 2D Sn-perovskite candidate with great potential in diverse optoelectronic devices. − The X-ray diffraction (XRD) patterns of (PEA) 2 SnI 4 thin films deposited from fresh and 3-day aged solutions exhibit stable layered structures with (002), (004), (006), (008), (0010), and (0012) peaks at 5.5, 10.9, 16.4, 21.9, 27.4, 33.0, and 38.7°, respectively (Figure a). A residual SnI 2 characteristic peak at around 25.6° was identified in the film from the fresh precursor solution, but it disappeared after 3 days of aging, indicating an incomplete reaction of precursor compounds in the fresh solution.…”