Improvement in Outcoupling Efficiency and Image Blur of Organic Light-Emitting Diodes by Using Imprinted Microlens Arrays

We demonstrated a new approach to fabricate microlens arrays attached to an organic light-emitting diode (OLED) to improve the outcoupling efficiency. Polydimethylsiloxane (PDMS) microlens arrays were fabricated by imprint lithography. Two kinds of photoresists were used to make a mold to imprint the microlens array. Using this simple and low-cost fabrication process, a maximum of 43% luminance enhancement was acquired with the green OLED. When attaching the microlens array to a green OLED, the efficacy and power efficiency were increased by 42% and 69% at 900 cd/m(2), respectively. The external quantum efficiency of the OLED with the microlens array was increased by 59% at 7.5 mA/cm(2) due to luminance enhancement at a large viewing angle without spectral change. Additionally, the image blur problem is quantitatively analyzed by defining blur width. The image blur problem induced by the microlens array is reduced by adopting the microlens array with lower height while the luminance enhancement by the microlens array remained.