Transparent and conductive electrodes by large-scale nano-structuring of noble metal thin-films

Abstract

The widespread use of transparent conductive films in modern display and solar technologies calls for engineering solutions with tunable light transmission and electrical characteristics. Currently, considerable effort is put into the optimization of indium tin oxide, carbon nanotube-based, metal grid, and nano-wire thin-films. The indium and carbon films do not match the chemical stability nor the electrical performance of the noble metals, and many metal films are not uniform in material distribution leading to significant surface roughness and randomized transmission haze. We demonstrate solution-processed masks for physical vapor-deposited metal electrodes consisting of hexagonally ordered aperture arrays with scalable aperture-size and spacing in an otherwise homogeneous noble metal thin-film that may exhibit better electrical performance than carbon nanotube-based thin-films for equivalent optical transparency. The fabricated electrodes are characterized optically and electrically by measuring transmittance and sheet resistance. The presented methods yield large-scale reproducible results. Experimentally realized thin-films with very low sheet resistance, Rsh = 2.01 ± 0.14 Ω/sq, and transmittance, T = 25.7 ± 0.08 %, show good agreement with finite-element method simulations and an analytical model of sheet resistance in thin-films with ordered apertures support the experimental results and also serve to aid the design of highly transparent conductive films. A maximum Haacke number for these 33 nm thin-films, ϕH = 10.7 × 10−3Ω−1 corresponding to T ≃ 80 % and Rsh ≃ 10 Ω/sq, is extrapolated from the theoretical results. Increased transparency may be realizable using thinner metal films trading off conductivity. Nevertheless, the findings of this article indicate that colloidal lithographic patterned transparent conductive films can serve as vital components in technologies with a demand for transparent electrodes with low sheet resistance.