1. Heeger Beijing Research and Development Center School of Chemistry Beihang University Beijing 100191 P. R. China
2. Department State Key Laboratory of Luminescent Materials and Devices School of Materials Science and Engineering South China University of Technology Guangzhou 510640 P. R. China
3. Department of Materials Science and Engineering College of Engineering Peking University Beijing 100871 P. R. China
4. Innovation Center for Printed Photovoltaics South China Institute of Collaborative Innovation Dongguan 523808 P. R. China