A study of photopatterning methods of silver nanowires and quantum dots for display application

Abstract

For the most promising patterning method for silver nanowires and semiconductors which are in the quantum confinement regime, a well-established photolithography method can provide many advantages such as high productivity, high resolutions, and scalability for practical applications. However, there are many challenging problems applying these nanomaterials on photolithography process: materials stabilizing during patterning process, dispersibility in wet-coating solutions, physical delamination due to chemical & mechanical instability. In this study, newly designed formulations consisting of water-insoluble polymers (polymethylmethacrylate (PMMA)) that has excellent optical transparency with low refractive index and photosensitive cross-linking agents in organic solvents are proposed for silver nanowire patterning using sonication treatment. After UV curing under photomask and development with organic solvent, substrate was treated by simple water wash and short sonication to clean AgNWs in the unexposed areas. Finally, a fine pattern of AgNWs protected with a crosslinked polymer matrix was obtained. Based on this study, it turned out that the width of the obtained AgNW patterns was in the range of 100 m to 3 m, and it was confirmed that the protected AgNW network maintained excellent mechanical stability even after taping and bending tests. As applications, this method was applied to the organic transistor which is the core component of the future flexile electronic device. Compared to 0-D structures (e.g. spheres, clusters), one-dimensional (1-D) nanowires with a high aspect ratio provide a better opportunity for connection between conductive materials when the electrodes are bent or elongated. To verify the usefulness of this patterning method, simple P3HT based organic field effect transistor was designed and fabricated, and then compared it with a reference device composed of Ag metal. For more applications to other nanomaterials, this study also proposes photopatterning methods of semiconductors which are in the quantum confinement regime. This study uses dispersion technology and binder chemistry. Studied dispersion methods with commercial dispersants and UV cross-linkable resins have verified high-loading QD blending and its photolithographic patterning applications. First of all, this study shows QD blending at low concentrations using QD powder and commercial dispersants. Then, it was further studied to prepare high loading QD blending (up to 30 wt.%) with additional additives. This QD formulations were tested to see its patternability and further confirmed changes in photophysical properties such as photoluminescence quantum yields (PLQYs), photoluminescence spectra, Full width at half maximum (FWHM), and optical properties retention during photolithography process. Finally, it shows a fine pattern images consisting of highly enriched QDs (20wt % and beyond), which can be potentially applied to color conversion films that converts blue light to red light or green light.