Improvement of Outcoupled Light Efficiency of Organic Light-emitting Diodes with a Use of Microlens Array

Because of a waveguiding effect and total internal reflection caused by a difference inrefractive indices, only 20% of generated light is emitted to the air and the rest is trapped or absorbed inthe device. An improvement of outcoupled efficiency of organic light-emitting diodes was studied using amicrolens array. Mold of microlens array was fabricated by using photo-lithography with the AZ9260photoresist, and the microlens array was formed onto the glass substrate using the UV curing agentnamed ZPU13-440. Device structure consists of microlens/glass/ITO/TPD/Alq3/LiF/Al. It was found thatthere is an improvement of external quantum efficiency by about 20% at the same current density for thedevice with the microlens array compared to that of the reference one. Simulated outcoupled efficiencyshows the improvement by about 20% for the device with the microlens array compared to that of thereference one. These results are consistent with the experimental ones