Enhancing Contrast Ratio and Efficiency in Top-Emitting Organic-Light-Emitting Devices by Using a Single Capping Layer

Conventional top-emitting organic light-emitting diodes (TEOLEDs) suffer from lower contrast ratio due to high reflection of semitransparent metal electrodes. Here, we demonstrated that coating a rubrene capping layer simultaneously enhances the electroluminescence (EL) efficiency and pixel contrast ratio (PCR) of TEOLEDs. By combining the rubrene capping layer’s absorption with the optical cavity configuration, we efficiently suppress reflections of TEOLEDs to ambient light. Meanwhile, rubrene-capped TEOLEDs exhibit significantly lower EL absorption compared to ambient light. With this strategy, rubrene-capped TEOLEDs achieve a 28.4% enhancement in external quantum efficiency (EQE) and a 22.6% improvement in PCR compared to conventional TEOLEDs, under 1000cd/ $\text{m}^{{2}}$ and 140 lux ambient illuminance. This approach has been proven to efficiently improve the PCR and EQE of TEOLEDs in bright environments.