Soft holographic interference lithography microlens for enhanced organic light emitting diode light extraction

Very uniform 2 mu m-pitch square microlens arrays (mu LAs), embossed on the blank glass side of an indium-tin-oxide (ITO)-coated 1.1 mm-thick glass, are used to enhance light extraction from organic light-emitting diodes (OLEDs) by similar to 100%, significantly higher than enhancements reported previously. The array design and size relative to the OLED pixel size appear to be responsible for this enhancement. The arrays are fabricated by very economical soft lithography imprinting of a polydimethylsiloxane (PDMS) mold (itself obtained from a Ni master stamp that is generated from holographic interference lithography of a photoresist) on a UV-curable polyurethane drop placed on the glass. Green and blue OLEDs are then fabricated on the ITO to complete the device. When the mu LA is similar to 15 x 15 mm(2), i.e., much larger than the similar to 3 x 3 mm(2) OLED pixel, the electroluminescence (EL) in the forward direction is enhanced by similar to 100%. Similarly, a 19 x 25 mm(2) mu LA enhances the EL extracted from a 3 x 3 array of 2 x 2 mm(2) OLED pixels by 96%. Simulations that include the effects of absorption in the organic and ITO layers are in accordance with the experimental results and indicate that a thinner 0.7 mm thick glass would yield a similar to 140% enhancement. (C) 2011 Optical Society of America