Composite polymeric:fullerene photovoltaic film enhances conversion efficiency
Organic photovoltaic cells composed of buckminsterfullerene (C60) blended with poly(2-methoxy-5-(2`-ethyl-hexyloxy)-1,4-phenylene vinylene), or MEH-PPV, show enhanced performance more than two orders of magnitude greater than MEH-PPV alone. Polymer-based photovoltaic cells could be economical to fabricate and easily tailored to specific applications. In the composite MEH-PPV:fullerene devices developed at the University of California, Santa Barbara, subpicosecond electron transfer from MEH-PPV (donor) to C60 (acceptor) increases the polymer photoconductivity. The structure forms a bicontinuous network of donors and acceptors, making it essentially a bulk heterojunction capable of high collection efficiency.
The group has fabricated several devices consisting of MEH-PPV:C60 composite layered on an indium tin oxide-coated glass or mylar substrate. A thin layer of aluminum or calcium provides the contact, and device sizes range from 1 cm2 to more than 15 cm2. Illumination intensities of 20 mW/cm2 at 430 nm resulted in energy conversion efficiencies of about 2.9%, more than two orders of magnitude higher than undoped MEH-PPV structures. Researchers expect these preliminary efficiency figures to double when device operation is optimized.