Inverted bulk-heterojunction plastic solar cells

Reversing the typical geometry of organic photovoltaic cells results in more environmentally robust devices. Plastic solar cells, or photovoltaic devices made from organic semiconductors, have demonstrated increasing efficiencies over the last few years.1 Several research groups have claimed devices with ∼5 % solar power conversion efficiency. And ∼5% efficiency has been certified at the National Renewable En-ergy Laboratory (NREL) on a device fabricated by the start-up company Konarka Technologies. While not yet sufficient for commercialization, these devices are approaching the 7–10 % ef-ficiency regime necessary for initial photovoltaic applications. As a result, research activity has intensified immensely in an ef-fort to take advantage of the potentially lowmanufacturing costs and ease of fabrication of these devices. One concern with plastic solar cells is their longevity. Plasti