1. Key Laboratory of Low-Grade Energy Utilization Technologies and Systems; Ministry of Education; School of Power Engineering; Chongqing University; Chongqing 400044 China
2. Key Laboratory of Optoelectronic Technology & Systems; Ministry of Education; Chongqing University; Chongqing 400044 China
3. Department of Materials Science and Engineering; National University of Singapore; Singapore 117574 Singapore