The thickness of a single Pb-Br slab is 0.59 nm for CsPbBr3 and, for CsPbI3, the single Pb-I slab is 0.62 nm thick. Considering these values, the thickness from the STEM images for all the samples corresponds to approximately four octahedron layers (n = 4). This thickness is overestimated because it does not reflect the absorption and PL spectra from Figure . We attribute this deviation to the tilt of the NPls (not perfectly perpendicular) when tracing their contrast profile, causing an artificial increase in the thickness. Subtracting this thickness from the interparticle distances found in the FFT images, we calculated the average length of the bilayer of oleylammonium cations to be 2.8 ± 0.2 nm, which is consistent with a previous report (~ 2.7 nm), while some other works report distances close to 3.5 nm. However, since the thickness of the PNPls is clearly overestimated (by at least the size of one monolayer), this value must be in between 2.8 and 3.5 nm.