| dc.description.abstract | In this study, both techniques of laser direct writing and electroless deposition are applied to the fabrication of flexible metal-mesh transparent electrodes. Due to the Gaussian distribution of the laser beam, the intensity of laser energy decreases gradually from the middle to the periphery, resulting in transversal temperature gradient and the Marangoni effect, which makes the crosswise profile of laser-sintered metal wire with uneven height profile, lower in the middle and higher at the two ends. Thus, the first part of this study explores whether electroless deposition can repair this uneven morphology. Results show that although the surface morphology before and after electroless deposition looks similar, the cross-sectional profile measurement shows that the height difference between the middle and the two ends becomes smaller. Hence, electroless deposition is a practical solution for repairing contour defects caused by Gaussian laser beam.
The second part of this study focuses on employing the electroless deposition technique to grow metal-mesh electrode from a glass substrate with an initial laser-direct-write seed pattern. The metal seeds are generated from a spin-coated composite thin film, synthesizing from silver nitrate (AgNO3) and polyvinyl alcohol (PVA) solutions, by laser direct write. PVA is capable of chelating silver ion and the silver ions are reduced to silver atoms via gaining and losing electrons as subjected to laser irradiation. In addition, the generated heat accelerates the reduction speed. The PVA/AgNO3 composite exhibits better film-formation property and the use of PVA increases the film’s linkage to substrate. Subsequently, that leads to good adhesion of the electrode to the glass substrate.
The resultant metal-mesh electrode, consisting of silver and copper, has sheet resistance about 1 Ω/sq and transmittance greater than 80%. But the height of the mesh line is about 1 micron which is too high to penetrate organic thin films in an organic device, where the film thicknesses are ranging from several tens to hundreds nanometers. Thus, in the third part of this study, we embed the electroless deposited electrode into a polyimide (PI) substrate as an embedded flexible electrode. Consequently, the surface roughness of the embedded electrode is less than 10 nanometers. The reciprocating bending test shows that, even under a small bending radius of 6 mm, there is only a 20% of increase in sheet resistance after 10000 cycles of bending.
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