Research
In recent years, with the desire to solve environmental and energy problems and build a sustainable society, society has high expectations for the use of solar energy. This research group is conducting research and development to create highly functional organic photoelectric conversion devices by creating and making full use of nanocarbon materials that have been given functions using chemical methods. Our research spans organic chemistry, inorganic chemistry, physical chemistry, and applied physics, and our research members engage in cross-disciplinary research while having discussions with each other.
Research on solar cells using carbon nanotube thin film transparent electrodes
Obtaining more natural energy through solar cells and other means has become a major research topic for researchers in this century in order to preserve the beautiful environment of the earth.
It is expected that by the end of this century at the latest, solar power generation will become the main source of energy generation, and that thermal power generation will supplement electricity during times when solar cells are not generating power. It envisions a society in which limited resources such as fossil fuels are utilized as chemical resources as much as possible, and electricity is generated by directly or indirectly utilizing solar energy. Against this background, research on solar cells has been actively conducted in this century. In addition to researching the structures of the materials and devices used to increase energy conversion efficiency, much research is also being conducted with an eye toward improving stability and lowering production costs for practical use.
Research and development of carbon nanotube thin film transparent electrodes for solar cells
The development of transparent electrodes using carbon nanotubes (CNTs) is an important research related to substrate materials for solar cells and other optoelectronic devices. Indium tin oxide (ITO) is commonly used as the substrate for organic and perovskite solar cells. However, ITO contains the rare metal indium and is expensive, which poses challenges in producing large-area solar cells and flexible solar cells. In our laboratory, we use the vapor phase growth eDIPS method to develop CNT substrates and fabricate CNT thin film transparent electrodes.
The dry process uses a floating catalyst/vapor phase filtration method to form CNT films, and there is no need to collect solid CNTs. This allows the CNT thin film transparent electrode to be formed directly on the filter.
In the wet process, highly crystalline and highly conductive Meijo eDIPS carbon nanotubes are used, CNTs are dispersed using a conductive surfactant, and a thin film is created by spray coating. This has the potential to result in more flexible and cost-effective transparent electrodes.
This research has the potential to provide sustainable substrate materials without the use of rare metals for the advancement of solar cell technology and the development of new energy conversion devices. We also believe that materials with excellent flexibility have the potential to be used in a variety of application fields.
Back electrodes made using the dry process of CNT (Carbon Nanotube) thin films have been suggested as promising alternative materials for various solar cell devices, potentially offering functionality equivalent to that of traditionally expensive materials such as gold and silver. Utilizing CNT thin films as back electrodes is a cost-effective and environmentally friendly option compared to the expensive gold and silver, with the potential to reduce the manufacturing costs of solar cells. Our laboratory has successfully achieved high open-circuit voltages in modular organic thin-film solar cells by applying dry CNT thin film technology. This success is attributed to the excellent conductivity and transparency of the CNT thin films, contributing to the improvement of solar cell performance. The application is promising for the development of various solar cell devices, including silicon solar cells and perovskite solar cells. In particular, its ease of transferability suggests it could be used as a high-performance intermediate or back electrode in silicon/perovskite tandem solar cells.
From the perspectives of environmentally friendly manufacturing and cost reduction, research into integrating CNT (Carbon Nanotube) thin films into solar cell devices is crucial. If this technology is commercialized, it can be expected to contribute to the spread of solar power generation and the development of sustainable energy sources.
The spray coating of CNT (Carbon Nanotube) thin films through a wet process, suitable for flexible patterning, offers many possibilities in the design and manufacturing of optoelectronic devices. CNT thin films are promising as bottom electrodes for organic and perovskite solar cells, as they meet both conductivity and transparency requirements. The ability to apply CNT thin films in various patterns through a wet process is considered beneficial for device design and efficiency enhancement. Enhancing the conductivity of CNT thin films is crucial for improving solar cell performance, so our laboratory is evaluating the introduction of carbon-based dopants into CNTs. This allows for the modulation of the electronic states of CNTs and enhances their conductivity. We are working on developing flexible solar cells by directly spray-coating CNTs onto PET (Polyethylene Terephthalate) substrates. This approach enables the creation of solar cells that can be bent or folded, contributing to the manufacture of flexible electronic devices.
These efforts are likely to contribute to the advancement of sustainable energy conversion technologies and the development of flexible electronic devices. Using a wet process improves flexibility, cost-efficiency, and manufacturing versatility, with potential applications in a wide range of fields.
Research and Development of New Solar Cells Using Next-Generation CNT Thin Film Transparent Electrodes
Using CNT thin films for both the bottom and top electrodes represents a significant step toward improving the efficiency of solar cells, enabling the absorption of more light and efficient photovoltaic conversion. Understanding the distinct characteristics of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) and exploring their combined use in layered solar cell structures are crucial for efficient energy conversion. Combining the properties of different CNTs allows for the tuning of the light absorption spectrum and charge transfer characteristics. Research into doping SWCNTs with materials that render them either n-type or p-type semiconductors, or incorporating organic semiconductor dyes, aims to enhance the photovoltaic properties of CNT solar cells. This could lead to improved electron conduction and carrier separation, potentially capturing energy from sunlight more effectively.
The development of “carbon-based solar cells” is an exciting endeavor to create energy conversion devices that are lighter, more flexible, and environmentally friendly compared to traditional silicon solar cells. Our research group is taking on the challenge of developing solar cells focused on nanocarbon materials.
Improvement of Durability in Perovskite Solar Cells and Application to Organic Light Emitting Diodes Using Fullerene Derivatives Capable of Vacuum Deposition
Research and Development of Fullerene Derivatives Capable of Vacuum Deposition
The synthesis of fullerene derivatives and their various applications are of great importance in organic electronics and energy conversion technologies. Fullerene (C60) itself is a significant organic semiconductor, but its properties can be tuned through chemical modifications, allowing for the creation of materials suited for further applications. Our research group has succeeded in synthesizing fullerene derivatives with attached organic groups. In particular, designing and synthesizing fullerene derivatives that can undergo sublimation purification at lower sublimation temperatures contributes to the improvement of the film formation process. Additionally, these modifications have led to enhanced light energy collection and electron transport, improving the performance of solar cells.
The efficiency and durability improvements in CNT-based organic solar cells using fullerene derivatives contribute to the evolution of sustainable energy conversion technologies. Furthermore, by working on the development of large-area, flexible organic photodiodes (OPDs), we contribute to the advancement of energy-efficient lighting and display technologies. Through these efforts, the design and synthesis of fullerene derivatives pave new possibilities in the fields of energy conversion technology and organic electronics.
Research on the Durability and Performance Improvement of Solid Polymer Fuel Cells Using Nanocarbon Materials
Research and Development of Fullerene Derivative Radical Quenchers for Improving the Durability of Fuel Cells
Solid Polymer Electrolyte Fuel Cells (PEMFC), which generate electricity from hydrogen and oxygen, are advancing towards practical use as a clean energy source for vehicle installation and home power supply. However, a significant challenge for the widespread adoption of PEMFCs is the durability of the Nafion membrane used in them. One cause of this issue is the chemical degradation by radical species generated from crossover hydrogen and oxygen leaking into the membrane. A key strategy for improving the durability of PEMFCs involves preventing radical attacks on the Nafion membrane.
Our research group is focusing on fullerene C60 as a radical quencher (scavenger) to prevent degradation of the Nafion membrane. We hypothesize that the hydroxylated fullerene produced when C60 quenches radicals can be reduced by crossover hydrogen, regenerating the π-conjugated system and thus sustainably quenching radicals. Based on this concept, we are designing and synthesizing fullerene derivatives that can be highly dispersed in the Nafion membrane and used as additives, aiming to realize high-durability fuel cells.
Research on High-Performance and High-Durability Fuel Cells Using Single-Walled Carbon Nanotubes (SWCNTs)
Polymer Electrolyte Membrane Fuel Cells (PEMFCs) are viewed as a promising sustainable energy conversion technology due to their high efficiency and low emissions, with the potential to reduce dependence on fossil fuels. However, the durability of platinum (Pt) catalysts and their support materials remains a significant challenge in the development of next-generation PEMFCs. Carbon Nanotubes (CNTs) are known for their excellent properties such as high electrical conductivity, high porosity, and high oxidation resistance, making them promising candidates as catalyst supports in PEMFCs. The high conductivity and porosity of CNTs contribute to the performance improvement of PEMFCs, while their high oxidation resistance and inert surface enhance durability.
Our goal is to synthesize metal nanoparticles of various shapes, sizes, and structures, particularly using Single-Walled Carbon Nanotubes (SWCNT) as catalyst supports, to achieve PEMFCs that are both high-performance and highly durable. Specifically, we aim to create catalyst materials, catalyst support materials, and catalyst layer structures that can achieve the ultra-high efficiency, ultra-high power output, and extremely long-term durability in high-temperature and high-potential environments outlined in the NEDO roadmap for PEFCs around 2040. Our research focuses on both scientific and industrial aspects, aiming to contribute to the advancement of technology in this field.
Synthesis, Physical Properties, and Thin Film Device Application Development of Mechano-Responsive Chromic Molecules that Change Absorption Color upon Pressure
Fundamental Research and Development and Application of Mechanochromic Materials
In the study of mechanochromism so far, discussions have primarily focused on changes in emitted colors, which were mostly qualitative. In contrast, we have developed mechanochromic molecules that change absorption colors and conducted quantitative research that discusses the relationship between mechanical pressure and color changes using numerical data, at the intersection of structural organic chemistry and mechanical engineering. Our laboratory discovered a force-chromic molecule called fluorenylidene-acridan, which changes its absorption color (visible color) under mechanical stress (compression). The color change is primarily related to the two stereoisomers of crowded tetrasubstituted alkenes. Compression induces a change from a bent conformation to a twisted conformation. In the twisted conformation, there is a charge transfer absorption from the electron donor to the electron acceptor site, resulting in a deep green color. Successful single-crystal X-ray structural analysis of both bent and twisted conformations has elucidated the reason for the charge transfer absorption in the twisted conformation. Secondly, the key to reversible color changes has been identified as the crushing of force-chromic molecular aggregates and their regeneration through contact with heat or solvent molecules, within the voids of the network structures of fibers and polymers. This has paved the way for the anticipated product applications of mechanochromic materials and provides a guideline for future foundational research on mechanochromic materials.
