"CELLULES GRAETZEL"
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.
