Close-packed hemispherical microlens arrays for light extraction enhancement in organic light-emitting devices

► We have fabricated close-packed hemispherical microlens arrays using a soft lithography method. ► The microlens contact angle and array fill-factor increase with polystyrene microsphere size. ► We have applied such microlens array to enhance light outcoupling in OLEDs. ► Up to 70% efficiency enhancement is achieved with the microlens array attached to OLEDs. ► Light outcoupling enhancement depends on the area and detailed structure of the OLED.