Improving Viewing\nAngle Characteristics of Top-Emission\nMicro-Cavity OLEDs with Randomly Distributed Micro Lens Arrays

To enhance the viewing angle and light extraction properties\nof\na top-emission organic light emitting diode (TEOLED) device without\ncausing severe degradation in the normal direction, we have adopted\nimprinting techniques to achieve improved reproducibility, throughput,\nand versatile utility for next-generation large display OLED panels.\nOur approach involves the use of dome-like corrugated substrates with\na randomly distributed microlens arrays mold. The randomly distributed\nmicrolens array patterns were successfully imprinted onto the glass\nsubstrate, achieving the intended scattering effects and extracting\ntrapped light of the surface plasmon polariton (SPP) mode. This resulted\nin a significant improvement in light outcoupling with the enhancement\nof viewing angles, leading to highly efficient red TEOLED. Notably,\nthese enhancements have led to a remarkable improvement in the viewing\nangle characteristics of the TEOLEDs as the reduced color coordinate\nshift (Δ<i>u</i>′<i>v</i>′)\nfrom 0.071 to 0.003 and a hypsochromic shift from 15 to 3 nm, even\nat angles up to 70°. Furthermore, the devices fabricated with\nthe imprinted random microlens array (IRMLA) substrate exhibited an\nimpressive 58% enhancement in external quantum efficiency (η<sub>EQE</sub>) compared to the reference device. Afterward, we discovered\na very powerful approach to enhance the viewing angle properties while\nsignificantly suppressing the decrease in light trapping in the fabricated\nTEOLED at the normal direction with the help of refractive-index engineering\nby filling optical adhesive in the air gap between the encapsulation\nglass lid and the OLED.