Spontaneously formed organic wrinkle structure for top-emitting organic light emitting diodes

Due to the imperfections of top metal electrodes, top-emitting organic light emitting diodes (TEOLEDs) suffer low efficiencies and non-uniform angular emission spectral characteristics. We demonstrate a novel and simple method of overcoming these drawbacks by directly forming wrinkles on the thin film encapsulation (TFE) surface of TEOLEDs. The developed method relies on the use of a liquid prepolymer that spontaneously forms randomly distributed micron-sized wrinkles upon exposure to ultra-violet light. The wrinkles contribute to the extraction of light confined in the air mode by widening the angle of the escape cone, leading to a 1.4-fold increase in the current efficiency. Due to the spatial randomness of the organic wrinkle structure, almost negligible spectral angular dependency was achieved. As a merit of the simple process at room temperature without complicated processes such as patterning and vacuum processes, the developed organic wrinkle structure can be directly used to enhance the characteristics of TEOLEDs, and is expandable to flexible OLEDs and various optoelectronic devices.