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

Close-packed hemispherical microlens arrays have been fabricated using a soft lithography method and used to enhance the light extraction efficiency in organic light-emitting devices (OLEDs). A close-packed monolayer of polystyrene microspheres was used to produce a soft template of polydimethylsiloxane for fabricating microlens arrays from a photopolymerizable optical adhesive. The microlens contact angle and array fill-factor increase with the polystyrene microsphere size, reaching (85 degrees +/- 5 degrees) and (85 +/- 3)% for 100 mu m size microspheres, respectively. Attaching such a large-area (2 cm in diameter) microlens array on the glass substrate of an OLED leads to up to 70% efficiency enhancement, which also shows dependencies on the area and detailed structure of the OLED. (C) 2011 Elsevier B.V. All rights reserved.