Direct Writing of Aluminum Doped Zinc Oxide for Optoelectronic and Energy Device Applications

Abstract

Micro scale patterning of transparent conducting oxide (TCO) offers great promise in producing efficient and low cost devices. Most of the major patterning techniques are either complex, expensive, non-scalable, or involve the use of environmentally unfriendly chemicals. Therefore, patterning of Aluminum doped Zinc Oxide (AZO) via sol-gel route, combined with direct writing, in particular, nozzle-based robotic deposition, offers a relatively easy and efficient way to selectively deposit complex features in digitally precise locations, at low cost and without excessive use of harmful chemicals. However, the printing process involves the interplay of various parameters, which need to be properly related, in order to annex the inherent benefits in the manufacturing process. Hence, the focus of this work is to investigate the influence of the printing parameters, which are viscosity, nozzle size, extrusion pressure, dispensing height and writing speed on the properties of the patterned AZO feature on glass substrates. The properties of interest include geometry of deposited and sintered feature, morphology, microstructure and electrical conductivity. A dual, three factors, three levels factorial experiment was designed to determine the influence of the printing parameters on the feature geometry. The morphology and crystal structure of the sintered feature at various combinations of printing parameters were studied by scanning electron microscopy (SEM) and x-ray diffraction (XRD). Also, the electrical properties of sintered feature with and without ultraviolet (UV) light irradiation were determined in a metalsemiconductor-metal configuration using a semiconductor analyzer. It was found that the main effects and interactions among the printing parameters considered were significant in determining the spread and the profile of the deposited features at 95% confidence level. A link between the printing parameters and the morphology and crystal structure was established, providing the opportunity for tailoring the deposited film to desired end use, without altering the chemical composition or post processing treatment. The electrical property, which increased upon UV excitation, was also found to be comparable with those reported in the literature for conventionally sol-gel deposited AZO films. Given the achieved control of feature geometry and microstructure through alteration of printing parameters, and the electrical conductivity of the deposited patterns, this work provides a pathway to efficient, large area optoelectronic devices at low cost. iii ACKNOWLEDGEMENTS I would like to express my sincere gratitude to my advisor, Dr. Kostas Sierros for his guidance and support through course of this program, and for always being committed to helping me succeed. His in-depth knowledge of the subject field has help me grow professionally. My sincere appreciation goes to Dr. Samir Shoukry and Dr. Charter Stinespring for agreeing to serve in my committee. Their relentless support and timely response is highly appreciated. I tha...

Engineered Inks for Environment-Friendly Additive Manufacturing of Hierarchical Microstructures

“…more material is deposited on the substrate). This relationship between the printing parameters, ink viscosity and final AZO dimensions has also significant effects on the resulting microstructure [131,190]; as can be seen from the XRD patterns, Figure 22. Briefly, the larger the printed feature width is, resulting from specific combinations of printing parameters and ink viscosities, the more random is the crystalline orientation of the AZO films.…”

“…The microstructural evolution of the printed AZO films (from the ink to the crystallized films), is of interest due to the anisotropic properties of ZnO [199], which could be targeted for specific applications. Thus, from the reported TGA profiles of the AZO inks ( Figure 24) [190], the inflection points At ~225, 420 and 500 °C indicate the temperatures at which the materials' most significant transformations occur. The inflection at 225°C may be attributed to the evaporation of organic species, whereas those at 420 and 500 °C correspond to the onset and end of ZnO crystallization, respectively [200].…”

“…The Al-doped ZnO (AZO) sol-gel ink system, consisting of Zn-acetate and Al-nitrate dissolved in 2-methoxy ethanol, and using ethanolamine as stabilizer, and PVP as viscosity enhancer; is used to investigate important interactions between the AZO structures' processing and microstructural properties. As highlighted in the work of Abidakun [190], the CDW printing conditions affect the morphology and crystalline structure of the AZO patterns. For this system, the variation of the printing parameters and viscosity properties of the inks resulted in variation of the preferential crystalline orientation of the patterned films.…”