## 3 Discussion  
To understand the processes leading to the PL intensity dependence on the environment in Sample #F and the origin of the strongly different behavior observed in Sample #A, it is first useful to remind that the PL intensity increase observed in both samples is qualitatively similar to the one reported both for lead halide perovskites polycrystalline thin films [22; 23; 24; 25] and single crystals [26; 27]. In all these systems, the PL intensity increase in WA has been ascribed to oxygen or moisture induced passivation of halide vacancies, which reduces the non-radiative decay rate, thus increasing the PLQY and the PL lifetime. In particular, in fully inorganic perovskites, the separate investigation of the role of the oxygen and of the moisture content allowed to conclude that the moisture effect is much weaker than the oxygen one [27]. On the contrary the few previous experiments on CsPbBr\({}_{3}\) NCs films evidenced a very different behavior, with the lack of any PL intensity variation due to the interaction with WA [27], or even an opposite PL intensity variation in WA (quenching instead of enhancement) [3; 28], ascribed to the lack of halide (Br\({}^{-}\)) vacancies on the NCs surface in the first experiment and to a different kind of defects on the NCs surface with respect to bulk polycrystalline films or single crystals in the second. The presence of PL enhancement in WA in our samples thus suggests that the co-precipitation growth method leads to the formation of NCs with a higher density of bromine vacancies on the surface with respect to NCs grown by hot-injection. It is also important to underline that the very high PLQY of the just deposited films and the relatively small PL intensity increase of Sample #F suggest a defect density much smaller than the one of bulk polycrystalline films and single crystals, typically showing much lower initial PLQY and much higher PL enhancement in WA [22; 23; 24; 25; 26; 27]. We also underline that the observed small red-shift and the narrowing of the FE and BE bands are consistent with previous results on MAPbI\({}_{3}\) thin films [24], ascribed to defects passivation without irreversible degradation. Further experiments, beyond the scope of the current paper, will be necessary to determine if this passivation is mainly due to oxygen or moisture. The analysis of the PL relaxation dynamics variation in WA allows gaining a deeper insight into the effects of the interaction with WA on the exciton relaxation pathways. In particular, the slight increase of the TR-PL peak value evidences the presence of a corresponding increase of the number of emitting sites (static interaction) [3], qualitatively consistent with the increase of the number of emitting grains observed in polycrystalline MAPbI\({}_{3}\) films in WA [22]. Moreover, beyond the static effects, the interaction with WA also modifies the PL relaxation dynamics, which become slower in WA. While this effect can be described as an average lifetime increase, also observed in MAPbI\({}_{3}\) films [23], our data evidence that this effect, in our sample, cannot be simply explained by the suppression of a non-radiative decay channel that increases the lifetimes. In particular, we observe that no variations are present both in the FE trapping lifetime \(\tau_{1}\) and in the FE relaxation time \(\tau_{2}\), while the variation affects the pre-exponential amplitudes, with a reduction of the FE trapping and the increase of the FE relaxation one. This result can be qualitatively ascribed to the complete passivation of defects in a part of the NCs, which then only shows FE recombination, indirectly confirming the low initial defects density. The interaction with WA also affects the BE contribution to the emission, with a clear increase of both the amplitude and of the decay times, evidencing the interplay between static increase of the number of emitting sites and dynamic suppression of a non-radiative decay process of BE.