[1] Niroo Res Inst, Chem & Mat Div, Nonmetall Mat Grp, Tehran 1468613113, Iran
[2] Univ Tehran, Nanophys Res Lab, Dept Phys, Tehran 14395547, Iran
[3] Natl Univ Singapore, Elect & Comp Engn, Singapore 119260, Singapore
[4] Singapore MIT Alliance Res & Technol SMART Ctr, Low Energy Elect Syst LEES, Singapore 138602, Singapore
[5] ASTAR, Inst Mat Res & Engn, 2 Fusionopolis Way,Innovis 08-03, Singapore 138634, Singapore
[6] Tech Univ Darmstadt, Inst Mat Sci, Alarich Weiss Str 2, D-64287 Darmstadt, Germany
[7] Univ Stuttgart, Inst Photovolta Ipv, Pfaffenwaldring 47, D-70569 Stuttgart, Germany