Flexible Tandem White Organic Light‐Emitting Devices with Over 46% External Quantum Efficiency via Integrating Efficient Light Outcoupling Structures

Abstract Flexible organic light‐emitting devices (OLEDs) are emerging as a cutting‐edge technology that revolutionizes displays and lighting panels to be lightweight, bendable, foldable, and even stretchable. However, they suffer from the poor light outcoupling efficiency due to the presence of various optical losses. Herein, a novel method of optical manipulation is proposed, which involves incorporating light‐scattering titanium oxide (TiO 2 ) nanoparticles (NPs) into flexible substrates, along with imprinting random micro‐lens arrays (RMLA) at the bottom of the substrates. Adopting the light outcoupling structures, the flexible single white OLEDs demonstrate a substantial improvement of 95.6% in the external quantum efficiency ( EQE ) compared to conventional flexible OLEDs, while maintaining a desirable spectral profile without any distortion. To further improve the optoelectronic performance, the light outcoupling structures are adopted in flexible tandem white OLEDs with two emission units, the maximum current efficiency is 147.8 cd A −1 , and the maximum EQE comes to 46.2%, which is 1.74 times higher than that of the flexible single OLEDs with the same light outcoupling structures. This work offers a convenient way to design flexible light extraction substrates for efficient wearable electronics.