Oh Young Kim

Solution Processed Blue Phosphorescent Organic Light Emitting Diodes Using a Phosphine Oxide Host Material

Solution processed high efficiency blue phosphorescent organic light emitting diodes were developed using a phosphine oxide derivative (SPPO1) as a host material. The SPPO1 was mixed with a polyvinylcarbazole (PVK), and the optimization of the device gave a high efficiency of 11.9 cd/A at . The reduction in the aggregation of the dopant, a smooth surface morphology, and improved charge balance were responsible for the high efficiency in the PVK:SPPO1 mixed host device.

P‐225: Suppressed Efficiency Roll‐Off in Phosphorescent Organic Light‐Emitting Diodes

Origin of efficiency roll-off in phosphorescent organic light-emitting diodes was investigated with triplet mixed host devices and stable devices with little efficiency roll-off was developed. Efficiency roll-off was significant in the device with narrow recombination zone and charge leakage out of emitting layer at high luminance was critical to efficiency roll-off. Efficiency roll-off could be reduced in triplet mixed host device with broad recombination zone and little charge leakage at high driving voltage. Triplet mixed host devices with an exciton blocking layer showed a quantum efficiency over 90 % of maximum quantum efficiency at a luminance of 20,000 cd/m2.

Effects of Chemically Surface Modified Lignin on Flexural Strength and Fracture Toughness for Lignin/Unsaturated Polyester Resin Composites

The lignin granule modified by allyltrimethoxy silane (VPS) was used to fabricate unsaturated polyester resin (UPR) composites as a reinforcing filler. The chemical surface modification of the pristine lignin granule was analyzed by FTIR and SEM/EDX. UPR composites reinforced by pristine lignin granule were prepared as the control samples and UPR composites reinforced by VPS-Lignin were prepared to study their flexural strength and fracture toughness behavior depending on the filler content. VPS-Lignin/UPR composites showed the better performance than of the pristine Lignin/ UPR composites in the mechanical properties (flexural strength and flexural modulus). And, the high values of the critical stress intensity factor (KIC) and the critical strain energy release rate (GIC) for VPS-Lignin/UPR composites implied the enhanced interfacial adhesion between UPR matrix and VPS-Lignin filler in the composites, which induced their enhanced fracture toughness.