We performed a fitting of the EPR spectra composed of radical species to understand the effect of the CsPbBr3 and Cs4PbBr6 NCs decomposition products on their shape. For all the fittings for CsPbBr3 and Cs4PbBr6 NCs, we consider a contribution of the BMPO/•OOH adducts. The summarized results, i.e., the spins, hyperfine values, and the areas used for the fitting, are presented in Tables S1-S4. The results of the fitting confirm the presence of Br, Cs, and Pb-related radical species, which indicates the decomposition of the CsPbBr3 and Cs4PbBr6 NCs. However, CsPbBr3