Abstract
Gallium-doped zinc oxide (GZO) and tin-doped indium oxide (ITO) nanoparticles (NPs) were combined to create bi-component suspensions for the drop-casting and CO2-laser sintering of transparent conducting oxide (TCO) thin films with significantly reduced ITO content. An aqueous dispersion of ITO NPs enabled the suspension of GZO NPs without surfactants. Transmission electron microscopy indicated the formation of high aspect-ratio segments of ITO NPs from the suspension through oriented attachment, that persisted in the deposited and sintered thin films to establish an efficient electrical percolating network within the less conductive GZO NP matrix. Rapid CO2-laser sintering under argon gas of approximately 800 nm thick NP films yielded resistivities of 7.34 × 10−3 Ω·cm and 116 Ω·cm for pure ITO and pure GZO respectively. However, a bi-component film with only 19.6 at.% indium (relative to zinc) achieved a resistivity of 3.21 × 10−1 Ω·cm. By changing the ITO content, the near-infrared transmittance could be adjusted between 13% and 82% and the optical bandgap energy between 3.93 and 3.33 eV, enabling fine-tuning of the properties. Finally, a fast and material/energy efficient processing route was demonstrated for the fabrication of a GZO-ITO circuit pattern using CO2-laser patterning of a mask and CO2-laser sintering of the NP films.
Highlights
Adopting the same CO2 laser source, we demonstrate a fast, additive patterning route for the fabrication of transparent conducting oxide (TCO) thin film tracks and circuit patterns, enabled through selective laser ablation of a polyester masking tape followed by drop casting of the NP dispersions into the openings
The thin film compositions are based on the Energy Dispersive X-ray (EDX) analysis data, while the In content of the dispersions are based on the initial formulations
We introduced a fast, scalable and material/energyefficient processing route to fabricate bi-component galliumdoped zinc oxide (GZO)-ITO thin films and tracks from NP suspensions in order to reduce the amount of ITO required to form these electrically conductive structures
Summary
The unsustainable supply and volatile cost of indium (In) have necessitated the search for strategies towards reducing indium consumption More sustainable alternatives such as galliumdoped zinc oxide (GZO) [9] and aluminium-doped zinc oxide (AZO) [10] have shown great promise. Königer et al [28] used a CO2 laser to sinter spin-coated ITO NP thin films in air, while Park and Kim [29] employed an excimer laser to anneal spin-coated ITO NP coatings in a nitrogen ambient They achieved electrical resistivities similar to those of furnace annealed materials, but in only tens of seconds. The desired interactions of the NPs need to be preserved throughout any patterning and other manufacturing steps These mixed materials and their processing are still relatively under-explored for the TCO systems, despite their technological importance and diversity in optical and electrical properties. The material combinations, together with the flexible deposition, patterning and laser processing methods, demonstrate excellent design freedom, low-cost, large scale integration possibilities and may be applicable to other TCO thin films systems
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