Interestingly, we can still observe some radicals even after 42 min of measurements (Figures S10a CsPbBr3 NCs. This is indicated by the rapid rise in the number of radicals for CsPbBr3 compared to Cs4PbBr6 NCs (Figure ). Besides the slower radical generation in Cs4PbBr6 NCs, their higher stability over time is reflected in their slower decay rate. activity of CsPbBr3 vs Cs4PbBr6 NCs is supported by the EPR analysis, where we find that the radical formation of CsPbBr3 is faster (Figures and). Moreover, using EPR kinetic analysis, we found that the decomposition of the NCs accompanies the radical formation, and this process is also much faster for CsPbBr3 NCs. Importantly, for both CsPbBr3 and Cs4PbBr6 NCs, the photocatalytic activity can be attributed to their role as sacrificial agents.