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Fabrication of Spherical Microlens Array Using Needle Coating for Light Extraction of OLEDs  

Kim, Juan (School of Energy Materials and Chemical Engineering, Korea University of Technology and Education)
Shin, Youngkyun (School of Electrical, Electronic & Communication Engineering, Korea University of Technology and Education)
Kim, Gieun (School of Electrical, Electronic & Communication Engineering, Korea University of Technology and Education)
Hong, Songeun (School of Electrical, Electronic & Communication Engineering, Korea University of Technology and Education)
Park, Jongwoon (School of Electrical, Electronic & Communication Engineering, Korea University of Technology and Education)
Publication Information
Journal of the Semiconductor & Display Technology / v.21, no.2, 2022 , pp. 25-31 More about this Journal
Abstract
By an aid of needle coating, we have fabricated a spherical microlens array using poly(methyl methacrylate) for potential applications in light extraction of organic light-emitting diodes. With an attempt to achieve high-density and high-aspect-ratio microlens arrays, we have investigated the coating behaviors by varying the material parameters such as the solute concentration and wettability of the poly(methyl methacrylate) solution and process parameters such as the dwell time of needle near the substrate, retract distance of needle from the substrate, and coating gap between the needle and substrate. Under the optimized coating conditions, it is demonstrated that high-aspect-ratio microlens arrays can be obtained using a coating solution with high solute concentration and a small amount of a hydrophobic solvent. It is found that the diameter and height of microlens array are decreased with increasing poly(methyl methacrylate) concentration, yet the overall aspect ratio is rather enhanced. By the addition of 5 wt% hexylamine in 35 wt% poly(methyl methacrylate) solution, we have achieved a spherical microlens with the height of 7.7 ㎛ and the width of 94.24 ㎛ (the aspect ratio of 0.082). To estimate the capability of light extraction by the microlens array, we have performed ray tracing simulations and demonstrated that the light extraction efficiency of organic light-emitting diode is expected to be enhanced up to 24%.
Keywords
Spherical microlens array; Needle coating; Aspect ratio; PMMA;
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