1. Department of Electrical Engineering; Princeton University; Princeton New Jersey 08544 USA
2. Department of Chemistry and Biochemistry; University of Arizona; Tucson Arizona 85721 USA
3. School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics; Georgia Institute of Technology; Atlanta Georgia 30332-0400 USA
4. School of Mechanical Engineering and Center for Organic Photonics and Electronics; Georgia Institute of Technology; Atlanta Georgia 30332-0250
5. National Center for Photovoltaics; National Renewable Energy Laboratory; Golden Colorado 80401 USA