After 3 min of illumination, the EPR spectra of CsPbBr3 NCs can be fitted with the contribution of Br and Cs radical species in addition to the •O2 -and without the contribution of Pb (Tables and). The hyperfine (a) value after 6 min of illumination indicates that the influence of Cs is significant in both Sol. 1 and 2, i.e., aCs = 1.457 and aCs = 1.393, respectively (Tables and).