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Organic thin film solar cell have advantages associated with lightweight, flexible, and low cost for both materials and fabrication processes. In addition, there is immense potential for improving or modifying the characteristics of the device, because of the endless possibilities offered by molecular engineering of the functional materials. As a result, research and development in organic thin film solar cells has continued to intensify all around the world, leading to vast improvements in performance, exemplified by achievements of power conversion efficiencies of up to 10%. We are studying basic science in the thin-film devices, requiring interdisciplinary study among organic, inorganic, physical chemistry and applied physics.

Studies on Organic Thin-film Solar Cells

  We are studying on organic thin-film solar cells through chemical approaches starting from design of the molecules. We design photoelectric properties and assembly structures of organic semiconducting materials, and synthesize such functional molecules. We also conduct device engineering to develop highly efficient and stable organic thin-film solar cells.


Synthetic Chemistry for Electron Donor Materials

  We are developing new tetracene and porphyrin derivatives that can absorb long-wavelength light and form supramolecular structure. We developed a tetracene-based low band-gap material having the imide group as an electron-accepting part and the disulfide group as an electron-donating part. This compound shows long-wavelength light absorption up to 850 nm. We are also investigating soluble porphyrin donors. Magnesium tetraethynylporphyrin derivatives are stable and soluble electron-donating materials that can be utilized to solution-processable organic thin-film solar cells. Coordination of solvent molecules to the central magnesium atom makes the compound soluble in common organic solvent. Magnesium porphyrinoids are found in chlorophyll that plays a key role in photosynthesis in nature.



Synthetic Chemistry for Electron Acceptor Materials

  Fullerene derivatives are good electron accepting materials because of their low-lying LUMO levels, small reorganization energy, and electron-delocalization ability. We focus on development of new fullerene derivatives that have high electron mobility, suitable LUMO levels for high open-circuit voltage, and self-assembling ability to achieve high-performance organic photovoltaic cells. We are also doing research on synthetic chemistry for fullerene derivatives and metal-fullerene complexes as well as application to switching photo-current conversion devices, liquid crystalline materials, single-molecular electronic devices, metal-carbon nanomaterials, and light-emitting devices.