# Experimental and Modeling Study for the Solar-Driven CO2 Electrochemical Reduction to CO
## 3 Results and Discussion  
### PV Characteristics  
The DSSC module, consisting of six individual cells connected in series using conductive silver paste, was characterized under varying irradiance levels, as shown in Figure 2.  
In Figure 2a, the I-V characteristics of the DSSC module vary according to the light intensity: in accordance with literature [23], the curve shifts to higher current-voltage regions with an increasing SUN of intensity.  
In particular, it can be noticed that both the short-circuit current and the open-circuit voltage increase with respect to the light intensity applied (Figure 2b) due to the higher photogeneration of carriers [24]. In particular, the open-circuit voltage in DSSCs is influenced by the potential difference between the dye's excited state and the conduction band of the TiO\({}_{2}\) and the electrolyte. When light intensity increases, more photons are absorbed by the dye, which leads to the generation of more excited electrons in the dye. This increases the amount of charge transfer to the semiconductor, which strengthens the electric field across the junction between the semiconductor and the electrolyte. A higher number of photogenerated electrons in the dye enhances the electrochemical potential difference between the dye and the electrolyte, which, in turn, increases the open-circuit voltage. Regarding the short-circuit current, it is directly related to the number of electrons injected into the  
Figure 2: I-V curves of the dye-sensitized solar cells (DSSC) module (**a**) and open-circuit potential (short-circuit current) (**b**) at different light intensities.  
conduction band of the semiconductor after the dye is excited by the absorbed photons, thus increasing with the increased number of electrons photogenerated.  
The experimental I-V characteristics (Figure 2a) are then fitted to extract the parameters for Equation (1) (Figure 3a,b), ensuring an accurate representation of the module's electrical performance.  
The I-V curves demonstrated the relationship between the incident power and the module's performance, highlighting the effects of the changes in both series and shunt resistances with the increasing light intensity, similar to the results already present in the literature [19; 20]. \(R_{sh}\) and \(I_{ph}\) show a decrease/increase with respect to the incident power, respectively, while \(R_{s}\) remains constant. The shunt resistance is mainly connected to the recombination of photogenerated electrons from the photoanode to the electrolyte redox mediator. A reduction in the \(R_{sh}\) at lower light intensities is consistent with a decreased amount of photogenerated carriers in the TiO\({}_{2}\), which are, therefore, extracted more efficiently from the photoanode and contribute to the external current. During the experimental conditions, a slightly lower temperature reached by the solar module at lower light intensities can also contribute to the reduction in the recombination reaction, resulting, therefore, in a lower shunt resistance. The series resistance, instead, arises mainly from geometric factors, electrical connections between the single DSSCs, and material properties, which are not dependent on the incident power.  
The diode equation (Equation (3)), filled with the fitted parameters, was subsequently used as an electrical source within the COMSOL(r) simulation framework. This incorporation allowed the model to predict the operational conditions of the integrated PV-EC system under real-world scenarios. In the simulation, the PV module provided the necessary voltage and current for the electrochemical cell, enabling the evaluation of system performance at the intersection of the PV and EC module characteristics.