F. Zhu, X. Chen, Z. Lu, J. Yang, S. Huang, and Z. Sun, “Efficiency Enhancement of Inverted Polymer Solar Cells Using Ionic Liquid-functionalized Carbon Nanoparticles-modified ZnO as Electron Selective Layer”, Nano-Micro Lett, vol. 6, no. 1, pp. 24-29, Dec. 2013.