## 4 Conclusions  
In conclusion, CsFAMAPbIBr perovskite-based devices showed different performance when using either SnO\({}_{2}\) or TiO\({}_{2}\) as ESC. SnO\({}_{2}\) as ESC showed higher electron collection efficiency and greater stability than TiO\({}_{2}\). However, when comparing fresh and aged devices, both ESC reveal a decrease in recombination, being the aging process favourable for the V\({}_{\text{OC}}\) enhancement for all the CsFAMAPbIBr devices. These results suggest that, after storing the devices under dry conditions, O\({}_{2}\) presents two main effects: the better extraction of charges because of the higher oxidation of spiro-OMeTAD, and the decrease in recombination due to its passivation effect over carrier traps. Interestingly, for the MAPbI\({}_{3}\) perovskite devices, the aging process did not have the same results. The hysteresis was almost identical for fresh and aged devices and with higher recombination after the exposition of the devices. This clearly shows that perovskite composition plays an important role in the dynamics of ionic and charge recombination, with MAPbI\({}_{3}\) having a greater ionic  
Figure 6: Carrier lifetime obtained from TPV decays as a function of the carrier density after the subtraction of the geometric capacitance for SnO\({}_{2}\)/CsFAMAPbIBr and SnO\({}_{2}\)/MAPbI\({}_{3}\) samples (**A**). TPV decays obtained during different times of illumination for fresh (**B**) and aged (**C**) SnO\({}_{2}\)/MAPbI\({}_{3}\). accumulation compared to CsFAMAPbIBr that leads to faster carrier recombination, and, consequently, worse device performances. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app12094545/s1](https://www.mdpi.com/article/10.3390/app12094545/s1)]([https://www.mdpi.com/article/10.3390/app12094545/s1](https://www.mdpi.com/article/10.3390/app12094545/s1)), Figure S1: Photovoltaic parameters of an average of 10 devices measured on fresh devices, and after 4 days, 1, 2, 4 (28 days), and 6 weeks for (A) SnO\({}_{2}\)/CsFAMAPbIBr, (B) TiO\({}_{2}\)/ CsFAMAPbIBr; Figure S2: Small perturbation lifetimes obtained from the exponential fitting of the TPV decays as a function of the light bias for the CsFAMAPbIBr samples deposited on top of TiO\({}_{2}\) (orange circles) or SnO\({}_{2}\) (blue diamonds) as ESC. The samples were measured fresh (filled symbols) and after the aging treatment (empty symbols); Figure S3: Capacitance obtained from the DiffCap method at different voltages (A) and after subtracting the geometric capacitance (charges accumulated at the contacts) (B). Charge density obtained at different voltages after the integration of the capacitance obtained with the DiffCap method, including carriers in the bulk and in the contacts (C). Charge density accumulated in the perovskite bulk (D). Small perturbation lifetime as a function of the total charge density accumulated in the device (charges in the bulk and in the contacts) (E). Small perturbation lifetime as a function of the charge density accumulated in the bulk of the perovskite. The lines represent the power law fitting \(\tau_{\Delta n}\)= \(\tau_{\Delta n_{0}}\left(\frac{Q}{Q_{0}}\right)^{-\lambda}\) used to calculate the recombination order (\(\delta=\lambda+1\)) of the devices (F); Figure S4: Total carrier lifetime (\(\tau=\tau_{\Delta n}\cdot\delta\)) as a function of the charge density stored in the bulk of the perovskite; Figure S5: Photovoltaic parameters of an average of 10 devices measured on fresh devices, and after 4 days, 1, 2, 4 (28 days), and 6 weeks for SnO\({}_{2}\)/MAPbI\({}_{3}\); Figure S6: Capacitance obtained from the DiffCap method at different voltages (A) and after subtracting the geometric capacitance (charges accumulated at the contacts) (B). Charge density obtained at different voltages after the integration of the capacitance obtained with the DiffCap method, including carriers in the bulk and in the contacts (C).