## 3 Results and Discussion
### Pristine Characterization
Moreover, the resistance \(R_{\text{S}}\) models ohmic contribution of the contacts and wires, \(R_{\text{HF}}\) is associated to carrier recombination, and \(R_{\text{MF}}\) and \(R_{\text{LF}}\) have been previously associated with several processes such as surface resistance, carrier accumulation resistance at the interfaces and slow processes, such as ion diffusion and trap-mediated charge recombination in the bulk [37; 42; 43]. In order to elucidate the physical processes governing the carrier dynamics at every time scale, a thorough analysis of the circuital parameters and their dependence on the \(V_{\text{OC}}\) was performed. Impedance spectra for different illumination intensities ranging from 0.1 up to 1-sun were measured at \(V_{\text{OC}}\) and fitted with the electrical equivalent circuit described above for the three thicknesses. Figure 4 shows the electrical parameters (resistances and capacitances), obtained from the fits versus \(V_{\text{OC}}\). Figure 3: Nyquist plot of the pristine samples. Experimental measurements (symbols), circuital fit (solid line). Equivalent circuital model used to fit experimental IS. As expected, we did not observe a significant dependence of the parameters on the active layer thickness, since ideally R and C depend on the active layer area but not on its thickness. However, in order to distinguish any slight dependence on active layer thickness, experimental data were analyzed separately when obtaining the ideality factor of the cells. The three resistive elements (\(R_{\text{HF}}\), \(R_{\text{MF}}\) and \(R_{\text{LF}}\)) show a negative exponential dependence on the \(V_{\text{OC}}\) (Figure 4a). From the dependence of \(R_{\text{HF}}\), traditionally associated with the recombination resistance, the ideality factor of the diodes was extracted. Values are shown in Table 1 as well as the ideality factor obtained from DC measurements (\(V_{\text{OC}}\) vs. illumination intensity [39]). \(R_{\text{LF}}\) shows a similar trend, and, according to [PERSON] et al. [43], both resistances are linked to the same physical process, thus, we also extracted the ideality factor from its dependence on \(V_{\text{OC}}\). Values are shown in Table 1. It can be observed that the ideality factors obtained from \(R_{\text{LF}}\), \(R_{\text{HF}}\) and DC measurements are similar, confirming the hypothesis that those parameters model the same dynamical process. These ideality factors range between 1.2 and 1.5, suggesting that Shockley Read Hall (SRH) recombination is the dominant recombination mechanism in the devices [44]. High and medium frequency capacitances remain almost constant with the irradiation level. Traditionally \(C_{\text{HF}}\) is related to the geometrical capacitance and its slight increase with \(V_{\text{OC}}\) could be due to thermal effects after being exposed to prolonged illumination [45]. On the other hand, low frequency capacitance, \(C_{\text{LF}}\), also exhibits an exponential dependence with \(V_{\text{OC}}\) (Figure 4b). From this dependence, we also calculated the ideality factor (see Table 1). These values are similar to those obtained from the high and low frequency resistances. According to [PERSON] et al. [43], this opposite behavior of the low frequency capacitance, \(C_{\text{LF}}\), and the resistances \(R_{\text{LF}}\) and \(R_{\text{HF}}\), suggests that these parameters are linked to the same physical process (carrier recombination). The physical meaning of the two resistances associated with \(C_{\text{LF}}\) remains unclear. The same authors suggest that these resistances might model different capturing processes for electrons and holes, respectively, to a surface recombination center, where the recombination event would finally take place.