Improving Viewing Angle Characteristics of Top-Emission Micro-Cavity OLEDs with Randomly Distributed Micro Lens Arrays

To enhance the viewing angle and light extraction properties of a top-emission organic light emitting diode (TEOLED) device without causing severe degradation in the normal direction, we have adopted imprinting techniques to achieve improved reproducibility, throughput, and versatile utility for next-generation large display OLED panels. Our approach involves the use of dome-like corrugated substrates with a randomly distributed microlens arrays mold. The randomly distributed microlens array patterns were successfully imprinted onto the glass substrate, achieving the intended scattering effects and extracting trapped light of the surface plasmon polariton (SPP) mode. This resulted in a significant improvement in light outcoupling with the enhancement of viewing angles, leading to highly efficient red TEOLED. Notably, these enhancements have led to a remarkable improvement in the viewing angle characteristics of the TEOLEDs as the reduced color coordinate shift (Delta u ' v ') from 0.071 to 0.003 and a hypsochromic shift from 15 to 3 nm, even at angles up to 70 degrees. Furthermore, the devices fabricated with the imprinted random microlens array (IRMLA) substrate exhibited an impressive 58% enhancement in external quantum efficiency (eta(EQE)) compared to the reference device. Afterward, we discovered a very powerful approach to enhance the viewing angle properties while significantly suppressing the decrease in light trapping in the fabricated TEOLED at the normal direction with the help of refractive-index engineering by filling optical adhesive in the air gap between the encapsulation glass lid and the OLED.