|dc.description.abstract||Flexible organic light emitting diode (OLED) devices may be used under long-term static bending in certain applications. The objective of this study is thus to investigate the effect of long-term static bending on the functional properties of barrier thin film and indium tin oxide (ITO) thin film in flexible OLED. In this study, a commercial barrier film, a commercial ITO/PEN sheet, and a commercial ITO/PET sheet are used. Encapsulation properties of the barrier film and electrical properties of the ITO/PEN and ITO/PET sheets are independently evaluated by conducting static bending tests at various radii of curvature. Moreover, characteristics of ITO thin film fabricated on PEN and PET substrates are also compared to assess the effect of substrate material.
For static bending of the barrier film, experimental results reveal that no significantly detrimental effect to the water vapor transmission rate (WVTR) at 40 °C and 90% RH is found for compressive bending up to 1,000 h and for tensile bending up to 100 h with a radius of curvature of 5 mm or above. However, WVTR of the barrier film is significantly increased and cracks are found in the barrier film when subject to tensile bending of a radius of 10 mm and 5 mm for 1,000 h. For mechanical testing of the ITO thin films under static bending, results indicate that no significant change in electrical resistance of the ITO/PEN and ITO/PET sheets is found for compressive bending after 1,000 h with a curvature radius of 10 mm or above. However, the ITO/PEN and ITO/PET sheets are seriously damaged under a tensile bending of 10-mm radius and 5-mm radius, respectively. The given ITO/PET sheet exhibits a greater resistance to long-term mechanical bending than ITO/PEN sheet in terms of change in electrical conductance, which is attributed to the effect of stiffness and thickness of substrate. As PET substrate has a lower stiffness and thickness than the PEN substrate, ITO thin film in the ITO/PET sheet has a smaller stress given a bending radius. Consequently, a smaller extent of change in the electrical conductance of ITO thin film is found in the ITO/PET sheet, compared to the ITO/PEN sheet.||en_US|