Polymer solar cells (PSCs) have potential to substitute for silicon-based solar cells due to low cost large-area vacuum-free printing technology. However PSCs for commercial use are limited due to low efficiency, furthermore sacrificing to their efficiency when only high work function metal, such as Al and Ag, as cathode is directly deposited or printed onto the active layer. To flexibly choose electrode materials and enhance the performance of PSCs, the modified layer such as LiF, SiOx, Au/LiF [l] was thermally deposited on top of active layers before depositing Al cathode. This successive vacuum deposition technique can greatly increase its cost of fabrication. To finally realize low cost and vacuum-free printing techniques for PSCs, solution processable materials, such as TiOx and poly(ethylene oxide), have been developed to modify the cathode, which can greatly improve the power conversion efficiency (PCE).