* Corresponding authors

^a Institute of Electronic Engineering, China Academy of Engineering Physics, Mianyang 621900, Sichuan, China

^b Key Lab of Organic Optoelectronics & Molecular Engineering of Ministry of Education, Department of Chemistry, Tsinghua University, Beijing 100084, China
E-mail: chldwang@mail.tsinghua.edu.cn

^c Department of Materials Science and Engineering, University of Washington, Seattle, WA 98195, USA
E-mail: gzcao@u.washington.edu

^d Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing 100085, China