1. School of Microelectronics, Beijing University of Aeronautics and Astronautics, No. 37, Xueyuan Road, Haidian District 100191, China
2. Key Laboratory of Low-Grade Energy, Utilization Technologies and Systems, MOE, Chongqing University, Chongqing 400030, China
3. Institute for Energy Research, Jiangsu University, Zhenjiang 212013, China