1. International Joint Research Center of China for Optoelectronic and Energy MaterialsSchool of EnergyYunnan University Kunming Yunnan 650091 China
2. Department of PhysicsYunnan University Kunming Yunnan 650091 China
3. Center for Optoelectronics Engineering ResearchYunnan University Kunming Yunnan 650091 China
4. Department of Materials Science and EngineeringYunnan University Kunming Yunnan 650091 China
5. Key Laboratory of Yunnan Provincial Higher Education Institutions for Organic Optoelectronic Materials and DevicesKunming University Kunming 650214 China
6. Department of Materials Science and EngineeringUniversity of Toronto Toronto Ontario M5S 3E4 Canada