The perovskite precursor preparation was conducted inside a nitrogen-filled glovebox at room temperature. 0.1M PEA2PbCl1Br3 stock solution was prepared by dissolving stoichiometric PEACl, PEABr, and PbBr2 in DMSO then left under continuous stirring for 2 hours. The precursor solution was then filtered with a 0.22 μm PTFE syringe filter before spin coating.