Efficient organic photovoltaic diodes based on doped pentacene

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Abstract
Recent work on solar cells based on interpenetrating polymer networks1,2,3 and solid-state dye-sensitized devices4 shows that efficient solar-energy conversion is possible using organic materials. Further, it has been demonstrated that the performance of photovoltaic devices based on small molecules can be effectively enhanced by doping the organic material with electron-accepting molecules5. But as inorganic solar cells show much higher efficiencies, well above 15 per cent, the practical utility of organic-based cells will require their fabrication by lower-cost techniques, ideally on flexible substrates. Here we demonstrate efficiency enhancement by molecular doping in Schottky-type photovoltaic diodes based on pentacene—an organic semiconductor that has received much attention as a promising material for organic thin-film transistors6,7,8, but relatively little attention for use in photovoltaic devices9,10. The incorporation of the dopant improves the internal quantum efficiency by more than five orders of magnitude and yields an external energy conversion efficiency as high as 2.4 per cent for a standard solar spectrum. Thin-film devices based on doped pentacene therefore appear promising for the production of efficient ‘plastic’ solar cells.