## 3 Factors of Wet-Type MCF Rubber Solar Cell
The piezoresistive resistance presented in the right ordinate in the figure denotes the specific resistance at non-irradiation. By changing the amount of Al\({}_{2}\)O\({}_{3}\) and TiO\({}_{2}\), we can change the specific resistance of the MCF rubber solar cell. From the figure, there is no correlation between photoelectricity and specific resistance. This typical tendency is different from the result of Figure 3. As a result, whether the specific resistance of the MCF rubber solar cell at non-irradiation is small or not, the photocurrent density does not usually become larger according to the amount of specific resistance. From the result of Figure 5, we can raise the question of whether a commercial pressure-sensitive electrically conductive rubber (PSECR) can be used as a wet-type solar cell. Figure 6 shows the photocurrent density to piezoresistive resistance for wet-type MCF rubber solar cells with Al\({}_{2}\)O\({}_{3}\) and TiO\({}_{2}\) when visible, and ultraviolet light were turned on, which are the same as those in Figure 5, compared to several PSECRs made of NR-latex produced by a Japanese company (B-1001 (Irumagawa Rubber Co., Ltd., Sayama, Japan), BMSE1-50 (Misumi Group Inc., Tokyo, Japan), AAH65032 (Shimonoseki Packing Co., Ltd., Shimonoseki, Japan), NR Sheet 65 (Fuso Rubber Co., Ltd., Hiroshima, Japan), REP-2 (Tigers Polymer Corp., Osaka, Japan)). On the PSECR as well as the MCF rubber, 0.22-g ruthenium complex dye and 7.4-g KI + I\({}_{2}\) were poured. The piezoresistive resistance of the abscissa represents the specific resistance for non-irradiation as described in Figure 5. Each colored rectangular indicates the range of values taken by several rubbers for each component. PSCERs are feasible for use in the production of a rubber-type solar cell. The photo-production procedure of PSCERs is based on the principle of the ordinary solid-state dye-sensitized solar cell, and the photoreaction process is established on each surface of the rubber: in terms of the electrochemical reaction generated by light, the photo-generated electrons are emitted from the dye pigment, and the oxidized dye is reduced by iodide ion I\({}_{3}\)\({}^{-}\) with the electrons circulated through the external circuit, as shown by Equations (12) and (13) in the first report [24]. This corresponds to the conduction of electrons and holes in the case of MCF rubber solar cells due to the photo-excitation generated in microscopic sections of the MCF rubber between the isoprene molecule, Fe\({}_{3}\)O\({}_{4}\) and TiO\({}_{2}\) particles. This is because the MCF rubber solar cell is a disorderly mixture of NR-latex and MF involving p- and n-type semiconductors and TiO\({}_{2}\), such as a colloidal suspension. In the case of PSCER, electrons and holes may be conducted throughout the material. Therefore, we can consider that there may exist the same conductions of electrons and holes in the inner PSCER as those in the case of the MCF rubber solar cell. Figure 6: Change in photocurrent density with piezoresistive resistance under visible and ultraviolet irradiation for PSCERs and wet-type MCF rubber solar cells with Al\({}_{2}\)O\({}_{3}\) and TiO\({}_{2}\) electrolytically polymerized under a magnetic field with Ruthenium complexes dye and KI + I\({}_{2}\) electrolyte. Each color indicates the range of values taken by several rubbers at each component. The abscissa in the figure presents specific resistance values at non-irradiation. In Figure 6, the photocurrent density does not necessarily become larger at smaller specific resistance such as that of the PSCERs, which is the same tendency shown in Figure 5. However, PSCER is harder than MCF rubber as shown by the results in Figure 7.  
Nevertheless, the MCF rubber becomes harder as increasing amounts of TiO\({}_{2}\) are incorporated.