Development of Laser Direct Reduction and Sintering Technology for Fabrication of Flexible Alloy-Mesh Transparent Electrode

With the market blooming of wearable electronics and the advent of OLED lighting and OLED flexibledisplay, a new wave of global demand in flexible transparent conductive films (TCFs) is to be set off. For thepast two decades, ITO and fluorine doped tin oxide (FTO) are the most often-used TCFs in industry. Indiumand fluorine are, however, toxic and environmental unfriendly. The indium element is rare in the earth stock.With the demanding growing, the cost of ITO is getting increase. Besides, the oxide coating is brittle and thediffusion of indium ions into the organic active layer might cause both the device’s performance and lifedegradations that further limit their applications to flexible and organic electronics. Due to its excellentdeductibility, chemical inert and high compatibility to the printing-based fabrication process, the metal-meshelectrode becomes a very promising alternative to the ITO electrode.This two-year termed proposal aims to develop the fabrication techs for flexible, multi-functionaltransparent alloy-mesh electrodes, targeting at the white OLEDs’ anode. The present challenges are to fulfillthe requirements of high transmittance (> 88% @ 550 nm), low sheet resistance (<10 /sq) and highflexibility as well as to achieve low surface roughness (Ra <15 nm). This flatness is difficult to be realized bythe current process for touch-panel based metal-mesh electrodes and is proposed to be accomplished throughthe method of embedded alloy-mesh electrode in this study. The alloy nanocomposite thin film, which isprepared from mixing the precursor of various metal ions (Cu, Ag, Au, and Zr, for examples) with polymer(PVA or PVP) solution, is prepared for patterning alloy meshes through the approach of direct laser inducedreduction and sintering. Furthermore, if molybdenum trioxide solution is involved, a multi-functionalalloy-mesh electrode is achievable. Because copper-mesh electrodes suffer from easy oxidation while silverandgold-mesh electrodes are expensive, an alloy-mesh electrode is a promising alterative because alloyshave been proved to have better mechanical and electrical properties as well as enhanced corrosion resistancecapability.From the viewpoint of applications, the laser-sintered metal-mesh electrodes possess good conductivity,transmittance and flexibility and have been proved to meet the requirements for white OLEDs. In the regardof fabrication techniques, the laser-based approach takes the advantages of being a mask-less, non-contactand eco-friendly process. Through incorporating the galvanometric scanner and x-y table, a large area ofmetal-mesh electrode is practicable. All fabrication steps are also executable in the ambient environment andat room temperature as well as are compatible to the printing-based process. These render this proposedapproach is an easy and low-cost method. In the academic side, usually, an alloy thin film is fabricatedusing the tech of thin film deposition in vacuum. Here we propose a brand-new approach that consists offorming a metal-contained nanocomposite thin film followed by reducing and sintering it using ultrafast laserpulses (ns-, ps- and fs- pulse durations, respectively). The microstructure of an alloy thin film sintered bysuch ultrafast heating and annealing process might be very different from those obtained from the usualvacuum deposition methods. By varying intensity and duration of laser irradiation, alloy thin films withdifferent microstructures are expected. The formation mechanisms are worthy to be addressed.