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Elastic Dry-Type Solar Cell Rubber with Photovoltaics and Piezoelectricity for Compressive Sensing
1  Faculty of Symbiotic Systems Sciences, Fukushima University


Ordinary solar cell is too hard to bend or be squashed by compression, and to be extended by tensile strength. Because it is generally made of plastic polymer. However, if the one has elastic, flexible and extensible property as well as sensing of piezoelectricity, it is useful and effective on the artificial skin installed over a human-like robot as a husk which generates electric power in itself by solar and perceives any forces or temperature. Or other varied engineering applications will be feasible. In addition, such hybrid functions of both photovoltaics and piezoelectricity does not need any power supply or battery to be equipped. The solar cell with sensing developed in the present paper is novel in solar cell and sensor fields. For the realization of the elastic solar cell, it was made of natural rubber and electrolytically polymerized with configuration of magnetic clusters of metal particles by aiding a magnetic field, corresponding to the MCF rubber which the present author had developed as an elastic, flexible and extensible sensor made of natural rubber. The principle of photovoltaics and piezoelectricity was elucidated. The photo-voltage and current were measured under the photo-excitation based on the p- and n-type semiconductor resulted from the electrolytic polymerization of MCF rubber or from the doping, or on the dye. For clarifying piezoelectricity the compressive sensing was measured under compression.

Keywords: Solar cell, Sensor, Natural rubber, Magnetic compound fluid (MCF), Elastic, Photovoltaics, Piezoelectricity, Magnetic field, Electrolytic polymerization
Comments on this paper
Hugo Avila-Paredes
some questions
Dear Prof. Shimada,
This is a very interesting project. I hope I didn´t overlook some information when reading your full paper; I got some questions:
1. What would be the appropiate values of photocurrent density and photovoltage for the proposed application?
2. Regarding the graph of photocurrent density vs time, why does the curve with purple symbols (Elec, mag, Ni, MF, NR-latex) does not have a null photocurrent at the beginning (when the light is off)?
3. How reproducible are the photocurrent and photovoltage results?
4. On the results of the effect of the compressive strain on the photovoltage (non mag), what could be the cause of the dispersion of values?
5. Have you performed experiments to evaluate materials degradation?
Thanks in advance.
Kunio Shimada
Thank you very much for your nice questions to my article. According to your suggested order, I'm willing to reply.
1. The purpose of the present article is elastic and elongatable solar cell with utilizing rubber. The most suitable method is refering to the concept of organic-type solar cell, especially Gratzel-type solar cell. The ordinary one is made of just plastic material, therefore, the present article is novel. These solar cell has such like the values presented in this article order on photocurrent density and photovoltage. However, I expect of obtaining more enhanced photocurrent density and photovoltage by utilizing other methods to be proposed in any future. Naturally I'm carrying out the investigation.
2. Not only the case of Elec, mag, Ni, MF, NR-latex but other cases are enable to have negative or postitive value of photocurrent at the beginning when the light is off. The cause is due to the behavior of built-in current. The ordinary semiconductor, in general, has built-in voltage because of oncoming plus and minus ions. At the present MCF rubber case, as numerous particles and molecules are dispersed, the built-in current also occures. In some of the pairs of oncoming ions, the electric relative position is reverse to the one of voltage owing to anode and cathode electrodes. We can obtain the built-in current and voltage as the sum of the pairs of oncoming ions, therefore, the photocurrent including the built-in current is enable to be not null when the light is off. The experimental data presented in the figure includes both buil-in and photovoltaic electricity.

3. The reproducibility depends on the rate of water involved in the MCF rubber. As decreasing water involved in the rubber, the photocurrent and photovoltage decrease. However, this phenomena is dry type without poring dye and electrolyte. In the case of wet type, dye-senstitized type, the photocurrent and photovoltage are repruducible because of the pouring of dye and electrolyte.
4. The cause is due to the dispersion of numerous particles and molecules as answered in the above question 2. The measued photovoltage is sum of the microscopic partial photovoltage of these many particles and molecules. However, the qualitative tendency can be acknowledged with slight variation.
5. The answer is corresponds to the one in the above question 3. Therefore, the wet type is suitable for avoiding the degradation.
Hugo Avila-Paredes
Thanks much for your reply and explanations