Semi-transparent metal electrode of Cu–Ni as a replacement of an ITO in organic photovoltaic cells

We demonstrate an indium-free organic photovoltaic cell that incorporates an ultrathin metal film as a semitransparent anode. In the proposed device structure, the indium tin oxide electrode is replaced by an ultrathin Cu–Ni bilayer. When an NiO is used as the hole transporting layer, the characteristic photovoltaic parameters of the cell fabricated with the metal electrode are similar to those of the device fabricated with the indium tin oxide (ITO). Despite the fact that the metal electrode exhibits a transparency that is 65% of the ITO electrode, the short-circuit current for the metallic anode based cell is 77% of the ITO based one, indicating that the photon absorption could be enhanced by the optical microcavity formed between the Cu–Ni and Al electrodes. The overall photo-conversion efficiency for the metallic electrode based cell is 76% of the ITO based one, which was measured to be 3.3%. The obtained performances of ultrathin metals when included in the cell architecture used here, combined with their low cost, high compatibility with other materials, and mechanical flexibility, confirm their potentials for organic photovoltaics.