Solar cells will be fabricated by a single organic semiconductor

The Institute for Molecular Science, National Institute of Natural Sciences announced on March 3, 2011 that a research group led by Professor Masahiro Hiramoto has succeeded in converting conduction-type of fullerene from n- to p-type by molybdenum oxide (MoO₃) doping. Details are published online in Applied Physics Letters on February 28, 2011.

Although organic thin-film solar cells are promising devices because of the advantages of being light weight, flexible and low cost, the conduction-type of organic semiconductors has not been controlled by doping impurities as is done in silicon. Two species of organic semiconductors, n-type fullerene (C₆₀) and p-type phthalocyanine (Pc), need to be used to form built-in fields in solar cells.

Researchers noticed that MoO₃ is used to raise holes in organic electroluminescent materials. They have succeeded in converting conduction-type of C60 from n- to p-type by co-evaporation of MoO₃ and C₆₀. Energetic value of the Fermi level, 4.60eV, for nondoped C₆₀ films measured by the Kelvin vibrating capacitor method was positively shifted to 5.88 eV by the co-evaporated doping of MoO3 at a concentration of 3300 ppm and approached the valence band of located at 6.4 eV. The upward bending of energy band in the Schottky junction formed at the interface between a metal (silver, Ag) and p-type C₆₀ film formed by MoO₃ doping was confirmed based on the photovoltaic properties. Organic solar cells could be fabricated by a single material - fullerene C₆₀.

More information: Masayuki Kubo, et al. "Conduction-type control of fullerene films from n- to p-type by molybdenum oxide doping", Applied Physics Letters Vol.98, No. 7, p. 073311 (2011); doi:10.1063/1.3556312 (3 pages); published online 18 February 2011.

Provided by National Institute for Materials Science