Semitransparent, thin metal grid-based hybrid electrodes for polymer solar cells

A conducting polymer/thin Au grid hybrid electrode was investigated to replace an indium tin oxide (ITO) electrode in polymer solar cells (PSCs). Semitransparent, thin Au films were combined with transparent conducting PEDOT:PTS films (70 nm thickness, ~90% of transmission), to form Au grid/conducting polymer hybrid electrodes. The mixed self-assembled monolayers coated on the Au grids and glass substrate provided uniform and adherent coating of conducting polymer on the monolayer, achieving a low contact resistance of 0.6 Ω mm. This resulted in a robust PEDOT:PTS/Au grid hybrid structure.Theoretical calculation showed the dependence of figure of merits (FM) on the filling ratio (=grid width/(grid spacing+grid width)) and Au thickness. In addition, grid spacing had an effect on the surface morphology of the conducting polymer; decreasing the grid spacing produced more flat surface of the overlayers, leading to enhanced performance of PSCs. The fabricated PSCs based on these hybrid electrodes showed that the best efficiency of 3.54%, comparable to that of devices based on an ITO electrode, was obtained at the filling ratio of 0.5 for 15 nm-thick Au electrodes, which was different from that predicted from the theoretical calculation, probably due to the grid spacing effects on the charge collection efficiency.