Study of Color Shift on the Periphery of Pixels Patterned by Laser Dye Diffusion Method in Polyermer Light Emitting Layer

• Main Authors: Hsiao-Wei Yu, 余曉薇
• Other Authors: Jeng-Rong Ho
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/35909567927245575881

碩士 === 國立中正大學 === 光機電整合工程所 === 96 === The available techniques for patterning polymer light emitting diodes (PLEDs) include the ink-jet printing, dye diffusion, micromolding in capillary, and micro-contact printing methods. The mechanism for driving the dye molecules to diffuse into the light-emitting polymer host is the concentration gradient and a thermal energy is usually employed to accelerate this process in fabrication. With suitable arrangement of dye concentration and temperature difference, the dye molecules can be locally diffused into a polymer film and formed the desired pixel patterns; and, through appropriate selection of the dye and the polymer, the resulting colors of the patterned pixel and the host can be organized. This study aims to address the issue of the color shifting occurring at the peripheral of a circular pixel, the peripheral ring, patterned by the laser dye diffusion method using a CO2 laser. Both the cause of the concentration difference aroused from the fabrication technique and the mechanism of color shifting due to the concentration difference were discussed. For the dye diffusion induced by laser irradiation, the Gaussian distributed laser beam profile resulted in the temperature in the central patterning area higher than the temperature at the peripheral region during the diffusion process that, eventually, gave rise to more dye molecules concentrating in the central area. The theory of energy transfer in a host-guest system was then employed to elucidate the color shifting due to the dye concentration difference and several PLED devices with different dye concentrations in the host polymer films were designed to verify the appropriateness of the employment of this theory. Finally, a PLED device with green pixels in a blue background, fabricated using the laser dye diffusion technique, was demonstrated. The idea of introducing a scarification layer using PVA (Poly(vinyl alcohol)) to buffer the laser energy and further protect the emitting material for a better resulting device performance was also exhibited.