[1] Pohang Univ Sci & Technol, Dept Elect & Elect Engn, Pohang 790784, South Korea
[2] Pohang Univ Sci & Technol, BK21 Program, Pohang 790784, South Korea
[3] Pohang Univ Sci & Technol, Dept Chem, Natl Res Lab Polymer Synth & Phys,BK Sch Mol Sci, Ctr Electrophoto Behav Adv Mol Syst,Grad Inst Adv, Pohang 790784, South Korea
[4] Pohang Univ Sci & Technol, Polymer Res Inst, Pohang 790784, South Korea