Polymer solar cells achieve 5.2% efficiency

Researchers from Wake Forest University (Winston-Salem, NC), Universidad Autonoma de San Luis Potosi (San Luis Potosi, Mexico), and New Mexico State University (Las Cruces, NM) have achieved what they claim to be the highest power-conversion efficiency so far reported for polymer-based solar cells: 5.2%.

Although polymer photovoltaic cell efficiencies have been greatly improved by the bulk-heterojunction concept-an interpenetrating network of nanoscale materials (such as fullerenes) that improve photon absorption and electron mobility-the “hopping” nature of electrons within disordered fullerene networks severely limits the obtainable efficiency. The researchers overcame this disorder by controlling the structure of the nanophase of the 120- to 170-nm-thick films through careful selection of the polymer/nanoparticle mixture ratio and controlled annealing procedures. As various fabrication parameters were changed, a near-field scanning optical microscope was used to understand how fullerene crystallization in the nanophase could be controlled to optimize performance. Polymer-based solar cells offer lower cost of fabrication, ease of processing, mechanical flexibility, and versatility of chemical structure compared to silicon-based solar cells. Contact David Carroll at carroldl@wfu.edu.