The capability of being processed by low cost, low temperature and efficient roll-to-roll printing processes on flexible
substrates has enabled the organic photovoltaic (OPV) solar cell to become a very promising technology for costeffective
and volume/weight-effective green energy harvesting [1-5]. Currently, indium tin oxide (ITO) has been used as
the transparent anode for OPV devices because of its excellent optical transparency in the visible range and acceptable
electrical conductivity. However, ITO is not an ideal material for flexible and low-cost OPV solar cell applications for its
poor mechanical properties [6, 7], and the shortage of indium. With the inherent advantages of excellent flexibility and
low-cost processes