Fabrication of copper window electrodes with ~10⁸ apertures cm⁻² for organic photovoltaics

A powerful approach to increasing the far‐field transparency of copper film window electrodes which simultaneously reduces intraband absorption losses for wavelengths 550 nm is reported. The approach is based on incorporation of a random array of ≈100 million circular apertures per cm2 into an optically thin copper film, with a mean aperture diameter of ≈500 nm. A method for the fabrication of these electrodes is described that exploits a binary polymer blend mask that self‐organizes at room temperature from a single solution, and so is simple to implement. Additionally all of the materials used in electrode fabrication are low cost, low toxicity, and widely available. It is shown that these nanostructured copper electrodes offer an average far‐field transparency of ≥80% and sheet resistance of ≤10 Ω sq−1 when used in conjunction with a conventional solution processed ZnO electron transport layer and their utility in inverted organic photovoltaic devices is demonstrated