Properties of Blade-coated Transparent Conducting Oxide Sol-gel Precursor Films on Plastic Substrates

The transparent conducting electrode (TCE) industry is dominated by indium-tin oxide (ITO) films deposited on glass for rigid applications and flexible polymers such as polyethylene terephthalate (PET) for flexible applications. These applications can range from liquid crystal displays to light emitting diodes to perovskite solar cells, most of which require electrodes with the maximum possible optical transmittance and the minimum possible sheet resistance. ITO films are generally deposited on their substrates via chemical vapor deposition or sputtering, both of which are low-throughput processes, on the order of 1 m/min web speeds or batch-processed at slower rates. This research presents a novel solution-deposition method for an alternative chemistry to TCE films. Solution deposition is advantageous over chemical vapor deposition and sputtering because it can be undertaken in an open air environment without much energy applied to coating. The project focuses on doctor blade coating as an intermediate step between current batch- processing methods such as spin coating and future roll-to-roll (R2R) compatible methods such as slot-die coating, in order to understand the dynamics of meniscus coating. The process entails synthesis, coating, and post-processing of indium-zinc oxide (IZO) sol-gel precursor ink on PET substrates. The benefit of this chemistry is its flexibility compared to ITO, its capacity for room-temperature solution deposition, and its decreased reliance on indium. The compositional ratio of In:Zn is 7:3, whereas that of ITO is 9:1 In:Sn. 0.2 M IZO alone is not sufficient to support the desired electrical conductivity, however, so a randomly oriented solution-deposited silver nanowire (AgNW) mesh layer is added to the IZO layer on PET. This results in the architecture PET/AgNW/IZO that has shown promising results in terms of transparency and conductivity. It is shown in this research that the PET/AgNW/IZO architecture is capable of performing within the range of figures of merit (FoMs) of commercially available PET/ITO and is processable at approximately ten times the speed. In addition to a deep exploration of the mechanisms at play during the blade coating process of each of these layers, this report includes a technoeconomic analysis comparing the two architectures and the costs of each in order to establish that blade coated PET/AgNW/IZO is less expensive to manufacture than PET/ITO is to purchase. This has implications for the TCE industry as throughput demands grow higher and higher as our society demands more high performance optoelectronics, and R2R solution processing is a suitable alternative.