Yun Cheol Han

Chitin Nanofiber Transparent Paper for Flexible Green Electronics

A transparent paper made of chitin nanofibers (ChNF) is introduced and its utilization as a substrate for flexible organic light-emitting diodes is demonstrated. Given its promising macroscopic properties, biofriendly characteristics, and availability of the raw material, the utilization of the ChNF transparent paper as a structural platform for flexible green electronics is envisaged.

Optical Effect of Surface Morphology of Ag on Multilayer Electrode Applications for OLEDs

We investigated the optical properties of a dielectric-metal-dielectric (DMD) electrode in relation to the surface morphology of Ag. We intentionally modified the number of voids and the surface coverage of the Ag layer. Normal and oblique incident configurations for transmittance measurement were employed to establish the relations between the Ag morphology and optical transmittance of the DMD electrode. For the configuration of MoO3/Ag/MoO3 (MAM), variation in the surface morphology of the Ag minimized the light scattering loss and the absorption of photons. This could lead to 18.6% enhancement of the transmittance at λ = 550 nm. The optical out-coupling was also enhanced in OLEDs, which was based on the MAM anode incorporating the continuous Ag film.

Reliable thin-film encapsulation of flexible OLEDs and enhancing their bending characteristics through mechanical analysis

Thin film encapsulation of flexible organic light-emitting diodes (FOLEDs) with a moisture barrier, incorporating a silica nanoparticle-embedded sol–gel organic–inorganic hybrid nanocomposite (S–H nanocomposite) and Al2O3 were demonstrated, and their reliability and mechanical characteristics were assessed. The bending stress of the multi-layer structure for both the case of moisture barriers and encapsulated FOLEDs was investigated based on nonlinear finite-element analysis (FEA). To minimize the bending stress at the desired region, the neutral axis (NA) position could be strategically adjusted by the introduction of a buffer layer of UV-curable cycloaliphatic epoxy hybrid materials (hybrimer), synthesized via a sol–gel reaction. The optimized multi-layer structure, proposed as a result of FEA was validated by related experiments. Regarding the bending characteristics of the moisture barrier structure, the water vapor transmission rate (WVTR) of the hybrimer-coated moisture barrier was much lower than that of a non-coated sample, as a result of calcium corrosion tests after bending. The structure of encapsulated FOLEDs, which are coated by the hybrimer achieved an almost identical performance to that of non-bending samples in spite of 30 days exposure to 30 °C and 90% R.H. after a bending test with a radius of 1 cm. During this period, the occurrence of dark spots caused by moisture penetration was effectively suppressed. Collectively, these results suggest that the bending characteristics of hybrimer-coated multi-layer structures are remarkably improved with the theoretical prediction of the NA position.