RESUMEN

Red, green, and blue top-emission organic light-emitting diodes (RGB TOLEDs) suffer from white color change with viewing angle due to the microcavity effect, called white angular dependence (WAD). Great efforts are devoted by applying various kinds of hazy films, but they suffer from poor mechanical stability and optical transmittance. Herein, we introduce an air-gap-embedded hazy film (AEHF) to solve these problems and suppress WAD in RGB TOLEDs. The AEHF is designed with optical simulation to realize high haze with transparency. By tuning geometries of the air gap inside the polymer, the AEHF realizes high haze of more than 90% in all RGB colors while maintaining high transparency. To experimentally demonstrate the AEHF, the O2 plasma is treated on a polymer film with AgCl as an etching mask to fabricate microstructures with high aspect ratios. Afterward, PDMS is coated on the patterned surface; air gaps develop spontaneously in the valleys between microstructures during the coating process. Using these processes, an air gap with 1.2 µm size and 400 nm period is formed inside the film and ∼100% haze is achieved while maintaining a high transmittance of 88%; these results agree well with rigorous coupled wave analysis results. By utilizing the AEHF into TOLEDs, the WAD can be drastically suppressed by 95.2% compared with that of a device without AEHF.

RESUMEN

We report a way to make an air-gap-embedded flexible film to reduce the screen-door effect (SDE) in virtual reality (VR) displays. Oxygen plasma was treated with a polyethylene terephthalate substrate to produce wavelength-scale micropatterns. These micropatterns induce an effective haze, but it is easily destroyed by a very small external scratch. Such a problem could be solved by coating the patterns with poly(dimethylsiloxane) (PDMS). The viscosity of PDMS, controlled by the ratio of the base and curing agents, plays a key role in determining the size of air-gaps at the valleys of micropatterns. As the ratio of base agent increases to 40, the average haze abruptly increased from 0.9% to 88.6% in visible wavelengths, while the average total transmittance maintained was between 89.8 and 91.7%. The origin of air-gap-induced haze is confirmed by numerical simulations. The hazy film remarkably reduced the SDE of the VR display from 30.27% to 4.83% for red color, from 21.82% to 2.58% for green, and from 26.02% to 3.38% for blue, as the size of air-gaps increases from 0 to 406 ± 91 nm. No defects were found after 10 000 bending cycles with a bending radius of 3 mm.

RESUMEN

We enhanced the optical transmittance of a multilayer barrier film by inserting a refractive index grading layer (RIGL). The result indicates that the Fresnel reflection, induced by the difference of refractive indices between Si(x)N(y) and SiO2, is reduced by the RIGL. To eliminate the Fresnel reflection while maintaining high transmittance, the optimized design of grading structures with the RIGL was conducted using an optical simulator. With the RIGL, we achieved averaged transmittance in the visible wavelength region by 89.6%. It is found that the optimized grading structure inserting the multilayer barrier film has a higher optical transmittance (89.6%) in the visible region than that of a no grading sample (82.6%). Furthermore, luminance is enhanced by 14.5% (from 10,190 to 11,670 cd m(-2) at 30 mA cm(-2)) when the grading structure is applied to organic light-emitting diodes. Finally, the results offer new opportunities in development of multilayer barrier films, which assist industrialization of very cost-effective flexible organic electronic devices.

RESUMEN

A variety of efficient green, yellow, and amber monochromatic phosphor-converted light-emitting diodes (pc-LEDs) were fabricated by simply capping a long-wave pass filter (LWPF) on top of LED packing associated with each corresponding powder phosphor. In this paper, the luminous efficacy and color purity of two green, three yellow, and two amber pc-LEDs were reviewed by comparing the optical properties and current/temperature stability of each LWPF-capped pc-LED. The simple combination of LWPFs and phosphor materials in the pc-LEDs provide a simple means of addressing the low luminous efficacy problem of III-V monochromatic semiconductor LEDs in the various colors of the wavelength range between green and amber (known as the "green gap"). This technique also represents a simple approach to mitigate the sub-linearity problem of the efficacy versus the driving current occurring at a relatively low current in III-V green LEDs (known as "green droop") to the level of a blue LED. This nano-multilayered filter-capped pc-LED can open further research into developing new color-converting materials (such as powder phosphors, and/or quantum dots) to extend the color palette in the wavelength region of the "green gap" and to improve the efficacy and color purity of color pc-LEDs.

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RESUMEN

This paper reports the possibility of a facile optical structure to realize a highly efficient monochromatic amber-emitting light-emitting diode (LED) using a powder-based phosphor-converted LED combined with a long-wave pass filter (LWPF). The capping of a blue-reflecting and amber-passing LWPF enhances both the amber emission from the silicate amber phosphor layer and the color purity due to the blocking and recycling of the pumping blue light from the InGaN LED. The enhancement of the luminous efficacy of the amber pc-LED with a LWPF (phosphor concentration 20 wt%, 39.4 lm/W) is 34% over that of an amber pc-LED without a LWPF (phosphor concentration 55 wt%, 29.4 lm/W) at 100 mA and a high color purity (>96%) with Commission International d'Eclairage (CIE) color coordinates of x=0.57 and y=0.42.

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RESUMEN

We demonstrate the combined effects of a microcavity structure and light-recycling filters (LRFs) on the forward electrical efficiency of phosphor-converted white organic light-emitting diodes (pc-WOLEDs). The introduction of a single pair of low- and high-index layers (SiO(2)/TiO(2)) improves the blue emission from blue OLED and the insertion of blue-passing and yellow-reflecting LRFs enhances the forward yellow emission from the YAG:Ce(3+) phosphors layers. The enhancement of the luminous efficacy of the forward white emission is 1.92 times that of a conventional pc-WOLED with color coordinates of (0.34, 0.34) and a correlated color temperature of about 4800 K.

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This paper reports a simple approach for the design of blue-excitation-light passing and phosphor-yellow-emission-light reflecting dielectric multilayers to recycle the backward emission of Y(3)Al(5)O(12):Ce(3+) (YAG:Ce) yellow phosphors on top of a blue InGaN light-emitting diode (LED) cup. The insertion of modified quarter-wave films of alternate high- and low-refractive index dielectric films (TiO(2)/SiO(2)) into the interface between a YAG:Ce phosphor layer and glass substrate resulted in 1.64 and 1.95 fold increase in efficiency and luminous efficacy of the forward white emission compared with that of a conventional phosphor on top of a blue LED cup with a lower correlated color temperature (< 4000 K).

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RESUMEN

We propose and demonstrate weak-microcavity organic light-emitting diode (OLED) displays with improved light-extraction and viewing-angle characteristics. A single pair of low- and high-index layers is inserted between indium tin oxide (ITO) and a glass substrate. The electroluminescent (EL) efficiencies of discrete red, green, and blue weak-microcavity OLEDs are enhanced by 56%, 107%, and 26%, respectively, with improved color purity. Moreover, full-color passive-matrix bottom-emitting OLED displays are fabricated by employing low-index layers of two thicknesses. As a display, the EL efficiency of white color was 27% higher than that of a conventional OLED display.

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RESUMEN

Utilizing the near- to far-field transformation based on the 3-D finite difference time domain (FDTD) method and Fourier transformation, the far-field profile of a photonic crystal organic light emitting diode is studied to understand the viewing angle dependence. The measured far-field profiles agree well with those of the simulation. The enhancement of the extraction efficiency in excess of 60% is observed for the optimized photonic crystal pattern.