Fig 7 - uploaded by Woo Jin Hyun
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EL spectra of OLEDs without and with regular and irregular microlens arrays at viewing angles of (a) = 0 and (b) = 30 .
Source publication
For the purpose of achieving high luminance, the introduction of microlenses could be a useful technique to enhance the light outcoupling efficiency because it can be easily applied to all types of lightings. However, the prevalent microlens arrays have been generally fabricated by
expensive and complicated photo-lithographic methods and have perio...
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Citations
... In 2013, Yan et al. [22] proposed a method to increase the coupling efficiency of the system by adding a square microlens array at the input and output terminal of the imaging fiber bundles. In 2014, Park et al. [23] proposed that microlens arrays may be an effective method to improve light coupling efficiency because of the easy application of microlenses in lighting systems. Experiments demonstrated that OLED with irregular microlens arrays have a 40% improvement in light coupling efficiency compared to conventional devices. ...
As the microlens array is attached to the infrared optical fiber imaging bundle, forming a rigid assemble is a new method to optimize the imaging quality of the infrared optical fiber imaging system. The alignment accuracy of the assembly is essential to the overall imaging quality of the system. To ensure that the assembly can still produce quality images under a certain alignment error, the imaging system model of assembly was established. Then introduced the concept of error margin and error margin coefficient to analyze the alignment error types and corresponding error effects of the assembly. Based on these concepts, the parameter design of the optical fiber imaging system was started. The limiting alignment errors were calculated at the error margin factor ξ = 1.25: transverse δ x = 9 μm , longitudinal dz = 50 μm , and deflection angle γ = 1.5°. Lastly, a ZEMAX simulation study was carried out. The simulation results showed that: under a certain alignment error, the light did not leak but be completely coupled into the core of the fiber, which confirmed the accuracy of error analysis and parameter design. And the assembly was realized in certain high-quality imaging under an alignment error. So the error analysis and parameters were designed correctly, and high imaging quality transfer of the system with a certain alignment error was achieved for the assembly.
A sandwiched color conversion layer (CCL) was prepared on the exterior of a blue organic light-emitting diode (BOLED) to achieve white luminescence. Inorganic red aluminate phosphor was used for color conversion. To enhance optical outcoupling, light extraction layers (LELs) of microlens-like SiO2 scattering arrays (SO-LEL) and a roughed-glass diffuser (rG-LEL) were prepared. The addition of an SO-LEL led to a directional radiation of OLED. A light extraction and scattering model for optical transmission through the SO-LEL was developed. However, the rG-LEL caused a slight broadening in the electroluminescence spectrum. The sandwiched CCL had functions of color conversion, scattering, and light extraction. The white OLED with a sandwiched CCL exhibited directional emission and high color stability along with an optical outcoupling enhancement of 39% in power efficiency and 31% in external quantum efficiency.
The use of polymer light-emitting diodes (PLEDs) as future displays and lightings has been of interest because of their advantages such as lightness, thinness, high contrast ratio, fast response time and high flexibility. Light-extraction structures such as microlens arrays have been designed to improve the efficiency of PLEDs. In this work, we have fabricated novel microlens arrays based on an organic-inorganic hybrid sol on a flexible substrate. Al2O3 nanoparticles dispersed in microlens arrays are expected not only to extract more light but also to block gas molecules. Further light-extraction from Al2O3 nanoparticles in the microlens arrays was confirmed by an increase in diffusive reflectance and photoluminescence intensity. As a result, the flexible PLEDs with the arrays showed enhanced maximum current efficiencies by 47% and 38% for SPB-02T (blue) and PDY-132 (yellow) emissive materials. They also showed improved stability, and high flexibility at a bending radius of 4 mm. Furthermore, Al2O3 nanoparticles were incorporated into irregular microlens arrays consisting of two different sizes of hemispherical lenses, to minimize changes in emission spectra and radiation pattern as well as to improve efficiency.
