## 2 Photovoltaics MCF Rubber Solar Cell
Second, we investigate the parameters of \(C\) and \(R\). As metal particles facing each other can be assumed to have the same charge as the parts of an \(n\)-\(p\)-type semiconductor, the dimensionless capacitance \(C_{n}\)* located at \(n\)'s turn is presented as Equation (3), where \(\varepsilon^{\prime}\) is the dielectric constant of the MCF rubber solar cell. The dimensionless capacitance \(C\)* of the MCF rubber solar cell is calculated as that at the outlet of \(n\) pairs of regions through which the electron transfers. As a result, \(1/C\)*\(R\)* is given by Figure 4 as an exponential function of \(cs\). \[C_{n}\)* = \frac{\varepsilon^{\prime n}}{2\sum\limits_{I=1}^{n}\frac{1+T_{j}^{3/4}} {\left(\prod\limits_{i=1}^{j}T_{i}\right)^{3/4}}} \tag{3}\]  
Figure 4: Theoretical results of \(1/C\)*\(R\)* to compression by tunneling theory. Figure 3: Theoretical results of dimensionless resistance to compression by tunneling theory. On the other hand, electric current \(I\) in the circuit of Figure 1 is presented as Equation (4) with dimensionless factors of \(C^{*}\) and \(R^{*}\), where \(t^{*}\) is the dimensionless time. The formula of Equation (4) presents that \(I\) is an exponential function of \(1/C^{*}R^{*}\). Figure 1:0  
By substituting the equation for \(1/C^{*}R^{*}\) shown in Figure 4 to Equation (4), we find that \(I\) contains an exponential function of \(cs\), and that \(I\) decreases with increasing \(cs\). The theoretical results qualitatively coincide with the experimental results obtained in the second report [19], in which the built-in current and photocurrent density decrease with increasing compressive strain. This tendency implies that the isolated layers of rubber or oleic acid among the particles and molecules in the \(n\)-\(p\)-type semiconductor dispersed in the MCF rubber solar cell are changed by compression. Therefore, we suggest that there exist thin layers among them. Based on this suggestion, we propose that \(I\) is presented by Equation (5) in the case of another equivalent electric circuit; it is usually introduced in ordinary solar cells as shown by Figure 5, where \(I_{S}\) is the reverse-bias saturation current, \(N_{d}\) is the diode ideality factor (=\(V_{f}/(V_{f}-V_{i})\)), \(V_{f}\) is the forward bias voltage, \(V_{i}\) is the voltage drop at the thin isolated layer, \(k\) is the Boltzmann constant, \(T_{a}\) is the absolute temperature, \(I_{ph}\) is the photocurrent, \(I_{d}\) is the diode current, \(I_{sh}\) is the shunt current, \(R_{sh}\) is the shunt resistance, and \(R_{s}\) is the series resistance. \(N\) denotes recombination in the \(n\)-\(p\)-type semiconductor; therefore, we can guess that in some of the \(n\)-type and \(p\)-type semiconductors of isoprene, oleic acid, and water molecules, the Ni particles recombine. Figure 1:1  
As a result, we can explain the photovoltaic property of the MCF rubber solar cell under elongation and compression by utilizing the equivalent electric circuit models shown in Figures 1 and 5 as follows. The isolated layers of rubber or oleic acid among the particles and molecules are not always thin; therefore, \(I\) is generally presented by Equation (6) from the Shockley diode equation and Ohm's law. As seen from the middle expression of Equation (6), the experimental data of the electric current \(I\) includes the photocurrent \(I_{ph}\) and built-in current, which depends on \(I_{d}\), and can be negative by the quantitative balance of \(I_{ph}\), \(I_{d}\), and \(I_{sh}\) under irradiation, as was presented in the previous two reports [17; 19]. \(I_{d}\) implies the dark current and is relevant to \(R_{sh}\). The dark current is generated by the influx of holes and electrons, which results from the existence of the depletion layer between the \(n\)-type and \(p\)-type semiconductors. \(I_{d}\) is a function of the diffusion potential \(V_{D}\), which is presented by the difference in electron affinity between the \(n\)-type and \(p\)-type semiconductors.