1. Beijing National Laboratory for Molecular Sciences Key Laboratory of Organic Solids Institute of Chemistry Chinese Academy of Sciences Beijing 100190 China
2. Materials Sciences Division Lawrence Berkeley National Laboratory Berkeley CA 94720 USA
3. Department of Polymer Science and Engineering University of Massachusetts Amherst Amherst MA 01003 USA
4. Tianjin Key Laboratory of Molecular Optoelectronic Sciences Department of Chemistry School of Sciences Tianjin University & Collaborative Innovation Center of Chemical Science and Engineering Tianjin 300072 China