Nanoarchitectonics Research Center of Japan's National Institute of Advanced Industrial Science and Technology (AIST) developed a light wavelength conversion material for use in crystalline silicon solar cells.
The wavelength conversion material uses europium (Eu) complex, a kind of metal complexes. The Center made a solar cell sealing sheet kneaded with the Eu complex and started the feasibility test focused on durability, etc.
The existing crystalline silicon solar cells have a higher power generation efficiency at around a wavelength of 750nm, the wavelength region of sunlight. Thus, the cells involve a problem in which all of the sunlight cannot be efficiently used because of the unused ultraviolet part (250-500nm). With the adoption of the latest material, it is possible to utilize a wider portion of the sunlight spectrum.
According to the Center (Highly Organized Molecular Nanostructure Team led by Dr. Masatoshi Kanesato), it discovered a promising material for Eu complex during the research of functional metal complexes that have organic molecules coordinated around the metal atoms. The Team discovered that the Eu complex has a function to absorb the ultraviolet part of sunlight and emits fluorescence after converting the UV part to the higher wavelength region.
The Team concluded that this wavelength conversion function can be utilized to enhance the efficiency of crystalline silicon solar cells and decided to start the investigation of its applicability. Thus far, seven patents have been applied for relating to this complex, according to the Center.
The Center determined that, in order to apply the Eu metal complex to solar cells, it is most effective to knead it into a sealing material of solar cells. Then, the Center launched a joint development with Sanvic Inc (Katsushika Ward, Tokyo), a manufacturer of solar cell sealing materials.
The two parties designed the molecule of Eu complex that can be kneaded into the sealing material, an ethylene vinyl acetate (EVA) sheet in particular, and optimized the molecule structure. They requested a chemical manufacturer to mass produce the Eu complex.
The powder of the Eu complex is kneaded into EVA beads and the beads are formed into sheets. Sanvic formed an EVA sealing sheet with a thickness of 0.6mm and a width of 115cm.
"We had difficulty in preventing the Eu complex from reacting with other materials mixed in EVA," Kanesato said.
AIST and Sanvic prototyped solar cells using the new EVA sealing sheet and installed them on the roof of Sanvic's Hosoe Plant (Hamamatsu City, Shizuoka Prefecture, Japan). A feasibility test to evaluate the durability, etc is now being conducted. The two parties confirmed that the generation efficiency of the solar cells was improved by 1.75% although the evaluation is still underway.
The Team also developed a rare-earth complex that emits red, green and blue fluorescent light. With three primary colors ready, the Team launched the development of ink for use in inkjet printers.