1. Center for Polymers and Organic Solids, University of California at Santa Barbara, Santa Barbara, California 93106-5090, United States
2. Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), Singapore 11760, Republic of Singapore
3. Organic and Hybrid Solar Cell Group, CSIR-National Physical Laboratory, Dr. K. S. Krishnan Marg, New Delhi 110012, India