Ultrathin Transparent Au Electrodes for Organic Photovoltaics Fabricated Using a Mixed Mono-Molecular Nucleation Layer

Abstract

A rapid, solvent free method for the fabrication of highly transparent ultrathin (∼8 nm) Au films on glass has been developed. This is achieved by derivatizing the glass surface with a mixed monolayer of 3-mercaptopropyl(trim­ethoxysilane) and 3-aminopropyl(trimethoxysilane) via co-deposition from the vapor phase, prior to Au deposition by thermal evaporation. The mixed mono­layer modifies the growth kinetics, producing highly conductive films (∼11 Ω per square) with a remarkably low root-mean-square roughness (∼0.4 nm) that are exceptionally robust towards UV/O₃ treatment and ultrasonic agitation in a range of common solvents. As such, they are potentially widely applicable for a variety of large area applications, particularly where stable, chemically well-defined, ultrasmooth substrate electrodes are required, such as in organic optoelectronics and the emerging fields of nanoelectronics and nanophotonics. By integrating microsphere lithography into the fabrication process, we also demonstrate a means of tuning the transparency by incorporating a random array of circular apertures into the film. The application of these nanostructured Au electrodes is demonstrated in efficient organic photovoltaic devices where it offers a compelling alternative to indium tin oxide coated glass.