1. Department of Physics & Astronomy and Wright Center for Photovoltaics Innovation & Commercialization; University of Toledo; Toledo OH 43606 USA
2. Center for Nanoscale Science and Technology; National Institute of Standards and Technology; Gaithersburg MD 20899 USA
3. Maryland Nanocenter; University of Maryland; College Park MD 20742 USA
4. Virginia Institute of Photovoltaics; Old Dominion University; Norfolk VA 23529 USA
5. Department of Materials Science and Engineering; University of Illinois at Urbana-Champaign; Urbana IL 61801 USA