Study on exploitation of near-infrared dyes for organic photovoltaic cells

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Highly conjugated organic compounds absorbing near-infrared light are essential materials for improvement of organic photovoltaic cells. In this study, we synthesize dyes with a novel skeleton bearing near-infrared absorption and investigate their electronic properties as well as potentials for organic photovoltaic-cell materials by the solution-processed fabrication of their precursors. When the two-dimensional πsystems such as porphyrins are fused with a benzene unit, there must be two major transitions: a longitudinal transition directed along the fused rings and short transitions due to the individual porphyrin rings. Therefore, strong absorption remains in a visible region, even if the absorption with the longest wavelength reaches to the near-infrared region. On the other hand, the πsystem of boron-dipyrromethene (BODIPY) spreads one-dimensionally and has one strong absorption band at ca. 500 nm. We succeeded in the synthesis of bisBODIPY dyes having absorption only in the near-infrared region due to the longitudinal transition by fusion of the BODIPY chromophores in the longitudinal fashion. In addition, we succeeded inthe preparation of stable near-infrared dyes under air by introduction of electron-withdrawing groups. Now, the application studies for near-infrared specific filters, organic photovoltaic cells, etc. are underway in the cooperative companies.