Seung-Yeon Kwak

Thermally Stable, Dye-Bridged Nanohybrid-Based White Light-Emitting Diodes

Thermally stable red and green light-emitting nanohybrids are introduced as an organic luminescent converter with broad color tunability and a high color rendering index for white light-emitting diodes (LEDs). Nanohybrid-based white LEDs are thermally stable and the color coordination is not changed by heat exposure.

Effect of Surface Energy on Pentacene Growth and Characteristics of Organic Thin-Film Transistors

Fluorinated hybrid materials were synthesized for a solution-processable gate insulator. The surface energy was modified by perfluoroalkyl chains contained in the hybrid gate insulator itself. We investigated the initial morphology and growth mode of pentacene and the characteristics of organic thin-film transistors (OTFTs) to determine how these characteristics depend on the surface energy. Pentacene growth was changed from a layer-by-layer mode to a three-dimensional (3D) island growth mode at low surface energy. Tightly and uniformly grown pentacene grains at 3D island mode induced good OTFT performance, but the carrier mobility was degraded at very low surface energy due to the large amount of grain boundaries.

High performance encapsulant for light-emitting diodes (LEDs) by a sol–gel derived hydrogen siloxane hybrid

The hydrosilylation reaction is a dominant curing method for the light-emitting diode (LED) silicone encapsulant, which requires characteristics of high transparency, high refractive index, and thermal stability against the LED junction temperature. In this research, we synthesized a hydrogen containing oligosiloxane resin through non-hydrolytic sol–gel condensation. Methyldiethoxysilane (MDES) and diphenylsilanediol (DPSD) were used as precursors and a non-hydrolytic sol–gel condensation reaction was performed under acidic conditions. The synthesized hydrogen oligosiloxane resin was mixed with a phenyl and vinyl containing oligosiloxane (PVO) resin, which was prepared by a sol–gel condensation between vinyltrimethoxysilane (VTMS) and the DPSD. This blended solution was cured at 150 °C for 4 hours to complete the hydrosilylation reaction. The cured material (phenyl hybrimer) shows low shrinkage during the curing reaction and provides excellent transparency (∼90% at 450 nm) and thermal stability (440 °C) with a high refractive index (n = 1.58 at 632.8 nm).

Thermally resistant UV-curable epoxy–siloxane hybrid materials for light emitting diode (LED) encapsulation

A UV-curable epoxy–siloxane hybrid material (epoxy hybrimer) was fabricated by photo-cationic polymerization of a sol–gel derived cyclo-aliphatic epoxy oligosiloxane (CAEO) blended with oxetane cross-linker in the presence of an onium salt. Antioxidants for fabrication of the UV-curable epoxy hybrimer with high thermal resistance against yellowing were incorporated in the UV-curable epoxy hybrimer. The UV-curable epoxy hybrimer with the antioxidants showed high thermal resistance without yellowing during 120 °C thermal aging. High thermal resistance of the UV-curable epoxy hybrimer was similar and higher compared to those of commercial thermally curable silicone and UV-curable epoxy LED encapsulants, respectively. The thermally resistant UV-curable epoxy hybrimer was successfully encapsulated on a LED without any cracking or delamination, and maintained a flat surface on the LED without distortion of the designed flat shape. Before/after thermal and blue light aging, the performance of the LED encapsulated by the UV-curable epoxy hybrimer was not changed. On the basis of its excellent properties as a LED encapsulant, the UV-curable epoxy hybrimer can be utilized as a UV-curable LED encapsulant for white LEDs.

Highly Condensed Fluorinated Methacrylate Hybrid Material for Transparent Low-k Passivation Layer in LCD-TFT

Photocurable and highly condensed fluorinated methacrylate oligosiloxane, with a low dielectric constant (kappa = 2.54), was prepared by a nonhydrolytic sol-gel condensation reaction. The oligosiloxane resin was then spin-coated, photocured, and thermally baked in order to fabricate a fluorinated methacrylate hybrid material (FM hybrimer) thin film. This study investigated the application of this FM hybrimer film as a low-kappa passivation layer in LCD-based thin film transistors (TFT). It was found that a dielectric constant as low as kappa = 2.54 could be obtained, without introducing pores in the dense FM hybrimer films. This study compares FM hybrimer film characteristics with those required for passivation layers in LCD-TFTs, including thermal stability, optical transmittance, hydrophobicity, gap fill, and planarization effects as well as electrical insulation.

Highly Condensed Epoxy−Oligosiloxane-Based Hybrid Material for Transparent Low-k Dielectric Coatings

A highly condensed epoxy-oligosiloxane resin was synthesized using a sol-gel condensation reaction of (3-glycidoxypropyl)trimethoxysilane and diphenylsilanediol in the presence of solvent. A higher degree of condensation and a larger molecular size of oligosiloxanes were achieved compared to a condensation reaction without the addition of a solvent. The epoxy-hybrimer coating film was fabricated by the spin coating and thermal curing of the synthesized oligosiloxane resin. The leakage current density and the dielectric constant decreased from 25.9 to 7.6 nA cm(-2) and from 3.16 to 3.03, respectively, by using the solvent in the preparation. The hybrimer coating film of a highly condensed oligosiloxane resin had a high transmittance of over 90% in a wavelength between 300 and 800 nm. Thus, the epoxy-hybrimer coating film can be utilized as the passivation layer in the thin-film transistor.

P‐19: Flexible Pentacene Organic Thin Film Transistors Using Sol‐Gel Hybrid Polymer Gate Dielectrics

Flexible organic thin film transistors (OTFTs) have been realized with sol-gel hybrid polymers (hybrimer) gate dielectric and poly(ether sulfone) substrate. The hybrimer thin films have good electrical and surface properties. OTFTs on polymer substrate exhibit good OTFT performance and small hysteresis.