Pattern fabrication of electroluminescent polymers using soft lithographic techniques

Abstract

Electroluminescence (EL) is the generation of light by electrical excitation. In detail, electrons and holes are injected from electrodes and captured each other, and then the excited electron-hole states, excitons, decay radiatively. For most practical applications, it is essential to fabricate micro-, or nano-scale emitting polymer in EL devices. Several methods have been used to pattern EL polymers previously: representatively photolithography and ink-jet printing. Although a small, monochrome, flat-panel display based on these materials has been demonstrated, each of these techniques has limitations that hinder the patterning of EL materials. Soft lithography uses a patterned elastomer, usually polydimethylsiloxane (PDMS), as the mold, stamp, or mask to generate or transfer patterns. In this paper, we describe the fabrication of patterned polymer microstructures using soft lithographic methods. First of all, we have prepared the patterned 1-dodecanethiol (DDT) self-assembled monolayer (SAM) on gold, 1-octylphosphonic acid (OPA) SAM on indium tin oxide (ITO), and 2-carboxyethylphosphonic acid (CPA) SAM on ITO by contact printing using the PDMS molds having relief structures. After forming patterned SAMs, the SAM-modified substrates were spin coated with EL polymer, poly(p-phenylenevinylene) (PPV), and then the hydrophilic region of the substrate was only coated with the solution. Therefore, the patterned PPV structures were obtained. As the second patterning method, substrates were directly contact printed with EL polymers, polydioctylfluorene (PDOF), PPV precursor, and poly(2-methoxy-5-(2``-ethylhexyloxy)-p-phyenylenevinylene) (MEH-PPV). The good pattern transfer of the relief structures in PDMS molds was formed for all the polymers. Finally, we have patterned EL polymers using micromolding in capillary (MIMIC). PDOF, PPV, and MEH-PPV microstructures showing high resolution were fabricated. In MIMIC, the viscosity effect on pattern resolution was investigat...