Yasuaki Ishikawa,
Doctor of Engineering and Associate Professor at Nara Institute of Science and Technology
Graduated from Department of Electronics, Faculty of Engineering, Doshisha University, in March 1997.
Then completed the latter period of his doctorate program at the Graduate School of Materials Science, Nara Institute of Science and Technology in March 2003 to receive his doctorate degree in engineering. Held postdoctoral positions at Institute of Physical Electronics, University of Stuttgart in April 2003 and Department of Physics and Astronomy, The University of Toledo in February 2005. Joined Sharp Corporation in October 2006.
Became an associate professor at the Graduate School of Materials Science, Nara Institute of Science and Technology in April 2010.
Associate Professor Yasuaki Ishikawa at Nara Institute of Science and Technology has been researching technologies to generate energy from solar light and indoor lights. Through his research and development of solar cells, he focused his attention on a new biomaterial that realizes dye sensitization. This new material is expected to advance bioelectronics further by helping create technologies for wearable solar cells and indoor energy harvesting equipment.
Dye-Sensitized Solar Cells, a Novel Material Different from Crystalline or Amorphous Materials
He has been researching "converting light to electricity," especially the development of solar cells. "When I was a high school student, I learned about the vast amount of energy Sun holds in a science magazine. I was emboldened by the dream that, one day, I would contribute to the advancement of mankind by pursuing research on solar energy," said Associate Professor Ishikawa. This dream became the driving force for him through his undergraduate and graduate programs. He then continued on with studies in Germany and the United States after receiving his Ph. D. After returning to Japan, he worked for a company well known for the development of solar cells, and became hired as an associate professor at the graduate school to engage himself in the development of solar cells to fulfill his dream.
His current research theme is "energy harvesting." It supplies energy to commonly used equipment through solar cells. These cells generate power efficiently from indoor lights without having to be placed in the sunlight. Dr. Ishikawa researches materials and processes for making solar cells that can efficiently generate electricity from, for example, indoor lights in a department store (illuminance of 500 to 1,000 lux with the energy of 5 to 10 W/m2) . He has also made actual prototypes.
For the past year or so, his attention has been focused on "dye-sensitized solar cells." They are made of a flexible new material different from crystalline silicon solar cells and non-crystalline (amorphous) solar cells, capable of being made as wearable solar cells. Associate Professor Ishikawa has received a grant from the Murata Science Foundation for the research target "Innovative energy conversion element based on low-energy consumption processes" and aims at utilizing this material to make solar cells.
What's Expected of Bioelectronics Using a Protein Supramolecule
Crystalline silicon, the most common outdoor type solar cell material currently, converts energy with high efficiency. Although amorphous silicon is used in some recent applications, its efficiency lags behind crystalline silicon. In terms of spectral sensitivity, crystalline silicon is near the solar spectrum while amorphous silicon is near the spectrums of common fluorescent light and white LED. In other words, amorphous silicon is the preferred choice for indoor power generation. Meanwhile, having characteristics between crystalline silicon and amorphous silicon, dye-sensitized material is capable of efficiently generating power indoors and outdoors. This ability makes it suitable for use as wearable solar cells in or out of buildings.
Its advantage is being able to be deposited at a low temperature unlike crystalline silicon materials requiring high temperature over 1,000°C. Dr. Ishikawa's current target is sub-100°C deposition. This will cut production cost significantly, since a large-scale production facility becomes unnecessary for low-temperature deposition. This fulfills another goal of realizing energy conservation in manufacturing processes. Developing solar cells with a low-temperature production process should contribute to consuming less energy.
Its advantage is being able to be deposited at a low temperature unlike crystalline silicon materials requiring high temperature over 1,000°C. Dr. Ishikawa's current target is sub-100°C deposition. This will cut production cost significantly, since a large-scale production facility becomes unnecessary for low-temperature deposition. This fulfills another goal of realizing energy conservation in manufacturing processes. Developing solar cells with a low-temperature production process should contribute to consuming less energy.
Future of Energy Harvesting Is Individualized Power Supply Through Solar Cells
There is a vast range of applications for dye-sensitized solar cells. Electric power can be generated by clothing-integrated solar cells indoors and outdoors to keep mobile phones and portable audio equipment charged. At hospitals, patients' conditions can be monitored continuously via solar cell-charged chips called smart patches. With their free-forming nature and pressure resistance, more applications are expected to emerge in the future. Dr. Ishikawa speculates, "Dye-sensitized solar cell technology is the strongest contender for indoor applications and clothing-integrated applications. To this end, we have set our current goals to be increasing its solar cell energy conversion efficiency and suppressing dye and electrolyte solution degradation."
Simultaneously with his research on dye sensitization, he is also working on improving the efficiency of non-crystalline silicon solar cell material called nanocrystalline silicon. Another one of his research themes is making energy-conserving solar cells over inexpensive plastic with low-temperature deposition. "Solar cells will be so much more useful if they can be made simply by sandwiching a solar cell material between plastic plates and baking it in a microwave oven, or spraying a material on something. Environment-friendly manufacturing and materials are in high demand now. We want to preserve the level of our current environment for our children's generation. I wish to contribute to the future through my researches as much as possible."
Enamored by solar energy, he entered the field of solar cell research. Murata is also keeping its eye on solar cell technologies as a strong candidate for its energy business expansion. We believe Dr. Ishikawa will continue to unravel new possibilities.
Development of solar cells produced with a low-temperature deposition
Both amorphous silicon solar cells and dye-sensitized solar cells are characterized by low-temperature deposition. Biomaterial called protein supramolecules are used for dye-sensitized solar cells. Titanium, after being absorbed by this material, is oxidized. This material is then dyed, injected with electrolyte solution and laminated.
Correlations between spectral sensitivity and light source spectrum of various solar cells
Spectral sensitivity and light source spectrum are correlated. Spectral sensitivity of crystalline silicon solar cells encompasses the solar light spectrum and above, while spectral sensitivity of amorphous silicon solar cells encompasses spectrums of fluorescent light and white LED. Dye-sensitized solar cell spectral sensitivity (for a common black dye) is between the two.
Dye-sensitized solar cell (on glass)
Dye-sensitized solar cells developed by Dr. Ishikawa can be dyed to various colors during fabrication. Although light-absorbing black is the most common color, it is possible to make red or blue solar cells.