New technique simplifies doping for organic semiconductors

A new solution-based method for introducing doping into organic semiconductor films could simplify the manufacture of efficient single-layer photovoltaic cells and move them closer to a commercial reality. Beyond solar cells, the doping technique could be more broadly used in other areas of organic electronics.
Developed by a team of researchers at the Georgia Institute of Technology (Atlanta; www.gatech.edu), along with partners at three other institutions, the technique could expand the potential applications for this technology, such as wearable electronics and small-scale, distributed power generation.
The process involves immersing organic semiconductor films into nitromethane solutions of polyoxometalates, which are polyanions containing transition metals (tungsten or molybdenum atoms, in this case). When exposed to the solution for several minutes, the metal atoms diffuse into the organic film, leading to efficient p-type (electron hole) electrical doping to a depth of 10–20 nm from the surface of the film, the researchers say.
“The p-doped regions show increased electrical conductivity and high work function, reduced solubility in the processing solvent, and improved photo-oxidation stability in air,” says the Georgia Tech team.
Electrical doping of organic semiconductors is traditionally accomplished using vacuum-based techniques, which require costly equipment. This solution immersion method provides a simpler alternative to air-sensitive molybdenum oxide layers used in the most efficient polymer solar cells, the researchers say.
Sponsored by the Office of Naval Research (Arlington, Va.; www.onr.navy.mil), the work was reported in a recent issue of Nature Materials. The research also involved scientists from the University of California at Santa Barbara, Kyushu University (Japan), and the Eindhoven University of Technology (the Netherlands).

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