## 4 Results and Discussion
### With Compressing  
Finally, we investigate the effect of compression on the photovoltage and photocurrent density due to irradiation by visible light in order to study the photovoltaics involving the piezoelectric effect. Figure 6 shows the photocurrent density and photovoltage extracted from the measured electric current  
Figure 5: Change in voltage and electric current density: (a) by turning visible light on and off; (b) by turning ultraviolet light on and off. Each color indicates a component of the MCF rubber solar cell of type (C). density and voltage in the case of the MCF rubber solar cell of type (C), made by \"twice polymerization\" under compression. The negatively changing photocurrent density and voltage was due to the change in the initial state, which is caused by the following physical mechanism. Because of the mixture of p- and n-type semiconductors and others, we can understand the position of A\({}^{-}\) and D\({}^{+}\) by the dispersion of particles and molecules as shown in (b-1) of Figure 1. The total change in the position of A\({}^{-}\) and D\({}^{+}\) occurs in reverse along the electric field lines due to the pressure. From the electron transfer theory in the field of macromolecular complexes, in the case of OSETR with weak interaction among particles of Fe\({}_{3}\)O\({}_{4}\) and Ni and molecules of polyisoprene, the resonance tunneling theory [26] or superexchange model [27] has been proposed as a well-known theoretical model. The latter is relevant to electron transfer between energy band gap of lowest unoccupied molecular orbitals (LUMO) and highest occupied molecular orbitals (HOMO) and ordinarily utilized to explain photoexcitation in solar cells. However, the tunneling theory is essential to explain the same, numerically. The material gap between p- and n-type semiconductors or A\({}^{-}\) and D\({}^{+}\) is an insulator with non-adiabatic process--it is through which an electron can jump to shift between different potential energy regions. The transfer of electric current in an MCF rubber made of silicon oil rubber solidified by drying without electrolytic polymerization has been investigated numerically by using the tunneling theory [28; 29]. The same theoretical formula can be applied to the present MCF rubber solar cell. As shown in Figure A1 in Appendix A, transfer of electric current is easier under compression because of the decreasing size of the gap. It explains the electric conductivity in a composite conductor composited in an insulator, or the piezo effect in the state before contact of each conductor by compression. The same shall apply for the piezo effect on the photoelectricity, as shown in Figure 6.  
The relation between the pressure and the compressive strain is also shown in the figure. There were two linear compressive regions with compressive elasticity, designated by I and II, and the latter had a slight nonlinearity because of the application of large compression, although, in general, there did not usually exist a plastic region in compression. The rigidity in \"mag.\" was larger than that in \"non-mag.\" because of the existence of Fe\({}_{3}\)O\({}_{4}\) and Ni particles as fillers. The photovoltaic effect was increased by compression from viewing the changes in the absolute values. The changes of the photovoltaic effect become larger with increasing gradient of the compressive strain to pressure and compressive Young's modulus. The magnitude of the pressure used in the present experiment is  
Figure 6: Change in photovoltage and photocurrent by pressure: “mag.”, with magnetic field at electrolytic polymerization; “no-”, without one. Each color indicates a component of the MCF rubber solar cell of type (C). important because the maximum pressure corresponds to the used force with 500 g weight, and it is a small pressure range. Regarding the effect of larger pressure on photovoltaic effect, it is dealt with in a consecutive report. In the case of no magnetic field applied under the electrolytic polymerization, no bulk hetero-junction structure was formed.