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

Abstract

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 degrees 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