[1] UNIST, Interdisciplinaiy Sch Green Energy, Ulsan 689798, South Korea
[2] Chinese Acad Sci, Inst Phys, Beijing Natl Lab Condensed Matter Phys, Beijing 100190, Peoples R China
[3] Chinese Acad Sci, Beijing Key Lab New Energy Mat & Devices, Key Lab Renewable Energy, Beijing 100190, Peoples R China
[4] Indiana Univ, Purdue Univ Indianapolis, Richard G Lugar Ctr Renewable Energy, Indianapolis, IN 46202 USA