## Effect of TiO\({}_{2}\) on Photovoltaics
### Experimental Photovoltaics  
Figure 3 shows the voltage, electric current, and electrical resistance as a function of the amount of TiO\({}_{2}\). In the images, \"on\" with a solid arrow indicates the onset of illumination and \"off\" with a dotted arrow indicates the termination of illumination. Voltage, electric current, and electrical resistance were measured separately. However, the tendencies of their correlation were obtained and were found to be larger with ultraviolet light than with visible light; that is, MCF rubber DSSCs reacted largely to ultraviolet light. Under illumination, the electrical resistance increased at the same time that the voltage and electric current increased as a photovoltaic effect. When the illumination was turned off, the electrical resistance decreased at the same time that the voltage and electric current decreased. The electrical resistance under illumination is relevant to microscopic behavior; extraneous electrons cannot be transferred among ionized particles and molecules. Therefore, when photoelectricity was enhanced by illumination, the electrical resistance increased. This behavior is further discussed below. In some cases, when the sample was first illuminated and the illumination was then turned off, it can be seen that the electric current changed rapidly and then returned smoothly to constant values; this occurred, for example, with the 3 g TiO\({}_{2}\) sample under visible light and the 4 g TiO\({}_{2}\) sample under ultraviolet light. This was due to dark current or leak current of the solar cells. The incidence of this phenomenon is subject to the varied conditions of the surface of the transparent glass and the MCF  
Figure 2: The surface of electrolytically polymerized MCF rubber with TiO\({}_{2}\): (**a**) anode side of the electrode during electrolytic polymerization with 2 g of TiO\({}_{2}\); (**b**) cathode side of the electrode during electrolytic polymerization with 2 g of TiO\({}_{2}\); (**c**) anode side of the electrode during electrolytic polymerization with 4 g of TiO\({}_{2}\); (**d**) cathode side of the electrode during electrolytic polymerization with 4 g of TiO\({}_{2}\). rubber during the fabrication of the solar cells, the ambience during fabrication, etc. Furthermore, it is impossible to predict the incidence; thus, certain precautionary measures must be considered. However, since this problem is often seen in ordinary solar cells, the same preemptive methods might be carried out. Figure 3: Effect of TiO\({}_{2}\) on the voltage, electric current, and resistance of MCF rubber DSSCs as a function of illumination vs. non-illumination: (**a**) voltage, visible light; (**b**) electric current, visible light; (**c**) electrical resistance, visible light; (**d**) voltage, ultraviolet light; (**e**) electric current, ultraviolet light; (**f**) electrical resistance, ultraviolet light. Incidentally, the surface of MCF rubber is dark brown, as shown in Figure 1, so that it can absorb light more effectively. Figure 4 shows the relationship between the electric current \(I\) and voltage \(V\) measured using a potentiostat (HA-151B, Hokuto Denko Co., Ltd., Tokyo, Japan) at 50 mHz scan rates in the potential domain of -1.5 to 1.5 V. As TiO\({}_{2}\) increased, the area surrounded by \(I\) and \(V\) decreases, and \(I\) in particular became larger at the largest \(V\). This means that the MCF rubber solar cell was close to the \(I\)-\(V\) curve of a photodiode [49; 50]. On the other hand, our previous study [32] clarified the characteristics of the photodiode under greater tension or compression. MCF rubber solar cells can typically be used as photodiodes. In order to make the characteristics of MCF rubber solar cells more similar to those of photodiodes, more TiO\({}_{2}\) might be used, as shown in Figure 4.  
The area of the \(I\)-\(V\) curve connotes the excited-charge regeneration. We can guess the effect of TiO\({}_{2}\) on the rate of excited-charge regeneration in the MCF rubber DSSCs.