## 3 Results and Discussion
### CsFAMAPIBr\({}_{3}\) vs. MAPb\({}_{3}\)-Based Devices on SnO\({}_{2}\) Layer  
Finally, as we have already observed in previous studies, perovskite composition also plays an important role in the dynamics of ionic and charge recombination [18; 21]. Therefore, we carried out the same studies on MAPb\({}_{3}\) fabricated on SnO\({}_{2}\) and compared them with those of the triple cation perovskite shown in Section 3.1. JV curves show that hysteresis after aging SnO\({}_{2}\)/MAPb\({}_{3}\) for 28 days was not reduced as it occurs for SnO\({}_{2}\)/CsFAMAPbIBr devices, showing a less positive effect from the aging process (see Figures 5A and S5, Table 2). There is an improvement in the fill factor occurring in the first days, but not in the V\({}_{\text{OC}}\) values, contrary to what we have observed for the triple cation perovskite composition. This reflects that carrier extraction might improve, probably due to the spiro-OMeTAD oxidation, with improvements in both conductivity and band alignment [17; 33], but carrier recombination might increase, as we observe even smaller values of V\({}_{\text{OC}}\) over the period of the experiment. The effect of aging on MAPb\({}_{3}\) was also confirmed in the V\({}_{\text{OC}}\) stability over time shown in Figure 5B, where, for both fresh and aged devices, the time to reach the maximum V\({}_{\text{OC}}\) was almost the same (approximately 10 s). These observations on the photovoltaic parameters might suggest that not all the perovskite compositions are valid for this dry air aging treatment. In previous publications, we already observed that the use of bromine-based compositions instead of iodine were  
Figure 4: TPV transients in logarithm scale obtained at different illumination times at 1 Sun intensity for fresh and aged CsFAMAPbIBr on TiO\({}_{2}\) (**A**,**B**) and SnO\({}_{2}\) (**C**,**D**) ESC. more prone to improve the photovoltaic parameters [34]. These results make us think that oxygen cannot passivate any defects at the MAPbI3 perovskite lattice, as we do not observe any long-term improvement in the photovoltaic performance. Then, we evaluate the carrier recombination kinetics for this composition using TPV and TPC. One thing that is clear is that with MAPbI3, there is a greater influence of the geometric capacitance on the differential capacitance technique, as it is shown in Figure S6, which might be attributed to an increased ionic accumulation at the interfaces [15; 35]. This bigger influence can lead to a wrong interpretation of the carrier recombination scheme (Figure S7). Therefore, to perform a correct analysis of the different perovskite compositions, we remove the geometrical capacitance component (Figure 6A and Figure S7). After doing this, MAPbI3 presents a faster carrier recombination than CsFAMAPbIBr, which would explain the lower values of VOC after the aging treatment. Although the recombination orders for SnO2/MAPbI3 were in the same order as those for CsFAMAPbIBr devices (\(\delta\) = 1-2), the recombination increased after 28 days instead of decreasing as for the other devices. Despite having discarded any benefits from oxygen exposure for MAPbI3 from the JV and VOC stability, we also measured TROTR (Figure 6B,C). Here, after 28 days of oxygen exposure, we observe a similar behaviour to TiO2-based CsFAMAPbIBr devices, as the negative component remains, but it is not as intense as in the fresh samples. While we