The new research findings has made the organic thin-film solar cells fabrication much easier. Earlier two kinds of organic semiconductors were needed; blending of fullerene with molybdenum oxide made where phthalocyanine use is not essential.
On March 3, 2011, The Institute for Molecular Science and the National Institute of Natural Sciences have announced that a research team guided by Professor Masahiro Hiramoto has doped molybdenum oxide (MoO3) successfully to convert conduction-type of fullerene from n- to p-type.
The advantages of the organic thin-film solar cells are light weight, flexible and low cost. As the silicon is controlled by doping impurities, it is not done in conduction-type of organic semiconductors. In order to create built-in fields in solar cells, the two types of organic semiconductors, n-type fullerene (C60) and p-type phthalocyanine (Pc), has to be used.
Researchers have observed that the holes in organic electroluminescent materials are raised by MoO3. Through the process of co-evaporating MoO3 and C60, conversion of conduction-type of C60 from n- to p-type is done. Kelvin vibrating capacitor method measures energetic value of the Fermi level, 4.60eV, for nondoped C60 films and is changed to 5.88 eV by the co-evaporated doping of MoO3 at a concentration of 3300 ppm and reaches the valence band at 6.4 eV. The energy band’s upward bending in Schottky junction is formed at the interface among a metal and p-type C60 film is based on photovoltaic properties. Fullerene C60 can be fabricated into organic solar cells.
Source: http://www.nims.go.jp/