Microlens array film fabricated by UV roll-to-roll nanoimprinting for enhancing out-coupling efficiency of organic light-emitting devices

Microlens arrays film fabricated by UV roll-to-roll nanoimprinting lithography is introduced on glass substrate to improve the out-coupling efficiency of organic light-emitting devices. The microlenses suppress wave guiding loss in the substrate and a theoretical model, based on Monto-Carlo model, is developed to simulate the enhancement effects. The numerical results show that ellipsoidal-like microlens array can increase the efficiency by a factor of more than 35% and the luminance density distribution along the orthogonal directions can be compressed by 10 degree. Such a microlens array mold is fabricated by a combination of DMD-based laser direct writing lithography and thermal reflow method, followed by electroforming for transferring the surface structure to a nickel plate. The obtained mold is wrapped on a roller for the mass production of microlens array film by UV roll-to-roll nanoimprinting process. OLED attached with such microlens array film with a maximum increase of 35% in efficiency is achieved and directional out-coupling phenomenon can be observed experimentally. Such a directional out-coupling microlens array film can be used to OLED to enhance the luminous intensity efficiency and save power consumption for future lighting and display application.