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 Al 2 O 3 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. Effective enhancement of the bending characteristics based on FEM analysis was demonstrated after reliable thin film encapsulation of flexible OLEDs.