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

Abstract

Very uniform 2 μm-pitch square microlens arrays (μLAs), embossed on the blank glass side of an indium-tinoxide (ITO)-coated 1.1 mm-thick glass, are used to enhance light extraction from organic light-emitting diodes (OLEDs) by ~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 μLA is ~15 × 15 mm 2 , i.e., much larger than the ~3 × 3 mm 2 OLED pixel, the electroluminescence (EL) in the forward direction is enhanced by ~100%. Similarly, a 19 × 25 mm 2 μLA enhances the EL extracted from a 3 × 3 array of 2 × 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 ~140% enhancement. Abstract: Very uniform 2 μm-pitch square microlens arrays (μLAs), 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 lightemitting diodes (OLEDs) by ~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 μLA is ~15 × 15 mm 2 , i.e., much larger than the ~3 × 3 mm 2 OLED pixel, the electroluminescence (EL) in the forward direction is enhanced by ~100%. Similarly, a 19 × 25 mm 2 μLA enhances the EL extracted from a 3 × 3 array of 2 × 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 ~140% enhancement. Keywords

Constrained Order in Nanoporous Alumina with High Aspect Ratio: Smart Combination of Interference Lithography and Hard Anodization

“…[ 32 ] However, when a pattern was desired in a metallic surface by LIL, typically hard or soft patterned stamps had to be fi rst fabricated by LIL and next the pattern had to be transferred into the metallic surface by wet or dry etching or nanoimprinting, approaches known as soft or hard interference lithography. [33][34][35] The direct application of LIL on aluminum (or any metallic surface) was restricted to extremely fl at surfaces and the patterning process could only be demonstrated on sputtered thin fi lms deposited on silicon wafers, which limited the maximum thickness (<1 μ m) of the porous membrane. [ 31 ] Only ultrathin AAO membranes with small pore aspect ratios (below 20) were feasible and the large versatility of these templates was lost.…”

Photonic crystal: energy-related applications

“…16 This was achieved with softlithography imprinting of very uniform 2-μm-pitch square arrays, embossed on the blank side of a ITO-coated glass. By placing a microlens array on the other side of OLEDs, trapped light inside the substrate can be extracted.…”

“…By placing a microlens array on the other side of OLEDs, trapped light inside the substrate can be extracted. 16 In general, methods to enhance light extraction of LEDs and OLEDs can be classified into two categories. One is texturing the surface of the lightemitting layer to extract light trapped inside.…”

Enhanced performance of organic light-emitting diodes (OLEDs) and OLED-based photoluminescent sensing platforms by novel microstructures and device architectures

“…To achieve better light extraction, various methods have been utilized, which can be classified into three major categories: (i) Modification of the emitting species, e.g., increasing the population of horizontally oriented emitting dipoles [73]; (ii) Modification of the ITO/substrate structure or interface [14,16,74,75]; (iii) Modification of the substrate/air interface [15,[76][77][78]. Recent studies have also shown that optimizing cavity effects and plasmon modes coupled with reflecting electrodes are also of major importance, affecting the outcoupling efficiency.…”