Modeling of flexible light extraction structure: Improved flexibility and optical efficiency for organic light-emitting diodes

Organic light-emitting diodes (OLEDs) have recently garnered significant attention due to their excellent performance. Despite intensive research efforts, OLEDs still face the challenges of low external quantum efficiency (EQE) and instability when applied to flexible displays. Herein, we developed a periodic flexible nano-grating structure (FNG) through laser interference lithography (LIL). Enhanced flexibility through the introduction of the FNG structure was modeled based on beam theory in terms of structure parameters and represented as the relative bending deflection. In addition, the structure parameters, period and thickness of the FNG structure were simultaneously optimized by computational finite-difference time-domain (FDTD) methods. The FNG structure not only enhanced the optical efficiencies of the device, but also reduced the stress of the flexible devices. Consequently, when the FNG with the largest relative bending deflection of 2.29 was applied to the OLED device, the external quantum efficiency (EQE) were higher as 2.80% compared to that of reference as 2.08%. After cyclic bending, the difference in EQE was more increased due to reduced relative bending stiffness, where the EQE of the FNG integrated device was 2.49% and that of the reference device was 0.91%.