Building on our previous work studying PEA2PbBr4 violet emitting perovskites and taking advantage of the perovskites' tremendous halide tunability, we replaced 50% phenethylammonium bromide (PEABr) with phenethylammonium chloride (PEACl). The molar ratio of the perovskite precursors with PEACl, PEABr and PbBr2, respectively, in DMSO was 1 : 1 : 1. The perovskite films were spincoated on quartz substrates and processed with a two-step annealing procedure according to our previous work. More details can also be found in the Methods section. The film shows a photoluminescent (PL) spectrum peak at 393 nm with approximately a 14 nm full-width half maximum (FWHM), which is shown in Figure . The perovskite films also have a strong excitonic band absorption peak at 382 nm, similar to the pure bromide 2D perovskite PEA2PbBr4 with an absorption peak of 402 nm. According to the feed ratio, we denote our new perovskite as PEA2PbCl1Br3. As shown in Figure , we believe that PEA2PbCl1Br3 should possess a 2D structure similar to that of PEA2PbBr4, where the [PbX6] (X= Cl or Br) octahedral layers are interspersed with organic PEA layers. This 2D structure is supported by X-ray diffraction (XRD) measurements. The XRD patterns in Figure confirm that PEA2PbCl1Br3 has a similar 2D structure to PEA2PbBr4 denoted by the signature (001) peaks. We also performed XRD fine scans from 4.8 to 5.8 degrees and from 15.4 to 16.4 degrees to enable detailed comparisons between PEA2PbCl1Br3 and PEA2PbBr4. No obvious peak shifts are observed in these two XRD spectra (shown in Figure and). Considering only a small portion of Br is substituted by Cl, this partial substitution may not be sufficient to cause a noticeable change in the crystal structures as observed through XRD. To further investigate the chemical composition of the perovskite films, X-ray photoelectron spectroscopy (XPS) was employed to discern the precise atomic ratio of chlorine to bromine. As depicted in Figure , the XPS spectrum allows us to elucidate the elemental constitution of the films. Furthermore, Figures and offer a detailed look at the binding energy regions corresponding to Pb 4f, Cl 2p, and Br 3p, respectively. Analysis of these spectra reveal that the atomic ratio within the as-synthesized perovskite films stands at Pb : Cl : Br = 21.8 : 17.3 : 60.9. This ratio aligns well with the intended stoichiometric feed ratio of Pb : Cl : Br = 1 : 1 : 3, confirming the accuracy of our fabrication process in achieving the desired chemical composition.