Having established the origin and behavior of the Si resistance under illumination, the appropriate EC can be determined to describe p-Si│a-TiO2│Pt devices operating in reverse-bias. First of all, despite having different protection layers, which has significant effects on the observed Nyquist plots, all devices have very similar onset voltages, fill factors and saturation currents, as shown in Figure . With similar current through all junctions at a defined voltage, it is expected that the resistances of all junctions will be similar. Referring back to Figure , this is only achieved when using the Maxwell circuit to model the device during EIS. Furthermore, the expected equality between the Si ac resistance and the dc resistance, regardless of illumination intensity, is only observed when using the Maxwell circuit (Figure ). Large deviations from this established behavior are observed if the device is assumed to operate according to the Voight circuit. Therefore, the data here confirm that the Maxwell circuit best describes the underlying operation of p-Si│a-TiO2│Pt devices performing the HER.