Hitachi Unveils Large Panel of Dye Sensitizing Solar Cells with High Efficiency

March 24, 2004 (TOKYO) -- Dye sensitizing solar cells made by Hitachi, Ltd are said to have caught up with amorphous Si solar cells in photoelectric conversion efficiency.
  Hitachi developed a prototype of a large panel of dye sensitizing solar cells, and unveiled them at the nanotechnology exhibition "nano tech 2004" held at the Tokyo Big Sight convention center March 17-19.
    The company exhibited a unit of four battery panels of about 10cm on a side connected together. According to the company, its photoelectric conversion efficiency was 9.3% in the lab, meaning "it is at a top level among the solar cells of the same type."
    The company's dye sensitizing solar cells have the following structure: organic dye is attached to titanium oxide (TiO2) that is made to be porous by coating and processing on a transparent electrode laid on a glass substrate, and is slipped in between the two opposing metal electrodes with an interval of just over 10um. The gaps in between electrodes are filled with iodine solution. When organic dye is subjected to light and electromotive force is generated, electrons run through the TiO2. When electrons run through the circuit and reach the metal electrode on the other side, they are received by ion I- in the iodine solution and change into I3-. This I3- transmits electrons to pigments, and electric current runs throughout the whole unit.
    This time, efforts were put into the TiO2 calcinations. The success is attributed to the joint research of Professor Motonari Adachi of the Institute of Advanced Energy, Kyoto University, and Hitachi.
    The key lies in the fact that by carefully controlling the calcinations temperature, the particle diameter of crystals is enlarged to around 10nm; and the larger the size of each crystal, the smoother the current. The finest result of calcinations was achieved at between +300 and +400 degrees Celsius.
    The photoelectric conversion efficiency of 9.3% is low when compared to the photoelectric conversion efficiency of existing popular Si solar cells, which ranges from 15% to 18%. However, the amount of current generated compares favorably with Si solar cells.
    "The efficiency is comparable with amorphous Si solar cells on the market," a company representative said.
    Problems include the durability of panels. However, the company says that the organic dye can be used for at least 10 years.
    "The melting temperature of Si is +1,400 degrees Celsius. Using this method, which enables production at from +300 to +400 degrees Celsius, the production cost can be reduced to around one-fifth of that of Si solar cells," the company said.

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