1. Department of Electrical Engineering Center for Advanced Photovoltaics South Dakota State University Brookings SD 57007 USA
2. Physics Department Faculty of Science Damietta University New Damietta 34517 Egypt
3. Tianjin Key Laboratory of Organic Solar Cells and Photochemical Conversion Tianjin University of Technology Tianjin 300384 P. R. China
4. Chemistry and Nanoscience Center National Renewable Energy Laboratory Golden CO 80401 USA