In this study, distributed Bragg reflector (DBR) structures are integrated into blue thermally activated delayed fluorescence (TADF) top-emitting organic light-emitting diodes (TEOLEDs) to improve both efficiency and color purity. The DBR structure, positioned above the underlying aluminum (Al) mirror of a conventional device, reflecting most of the emitted light before it reaches the Al mirror and achieving nearly 90% reflectivity in the blue region. The structure consists of alternating silicon nitride (high-refractive index) and silicon dioxide (low-refractive index) dyads, with layer thicknesses calculated for a target wavelength of 480 nm. This configuration suppresses lossy surface plasmon polariton modes at the Al-mirror surface while enhancing the microcavity resonance. Optical simulations show that a 4-dyad DBR reduces the full-width at half-maximum (fwhm) and shifts the emission peak toward shorter wavelengths. Experimentally, at a current density of 3 mA cm-2, the 4-dyad DBR device exhibited simultaneous enhancements of 34.5% in external quantum efficiency, 18.95% in current efficiency, and 24.87% in power efficiency compared with the 0-dyad reference device. Additionally, the emission peak exhibited a 4 nm blue shift, and the fwhm decreased by 60.7% (to 22 nm). Overall, DBR integration enables improved efficiency and color purity in blue TADF TEOLEDs.

Low-haze light extraction from OLEDs was achieved using nanoscale corrugation fabricated via plasma treatment. The irregular nanostructure (INS) showed 1.6% haze, comparable to bare glass, with 10% angular-integrated intensity enhancement. Modulating refractive index by gas type and treatment time enables application to broad-spectrum, flexible OLED displays.

We report a flexible/detachable film with high-refractive-index particles and green-QDs to improve the light extraction efficiency of OLEDs. The fabricated film was attached to the outside of the blue-OLEDs, and the external light extraction efficiency was improved by approximately 22.3% while simultaneously color-conversion.

In this study, we fabricated a nanostructure on the surface of the micro-lens array (MLA), which is one of the light extraction technologies of organic light-emitting diodes (OLEDs), by performing the Reactive Ion -Etching (RIE) process. The MLA consists of a lensed area and a lens-less bottom (flat film area). We performed a systematic analysis to find ways to improve the light extraction efficiency of the MLA surface and flat film area. By controlling the RIE process time and type of gas plasma, nanostructures were formed on the surface of the MLA. O2 and CF4 gas plasmas resulted in nanostructures with tall heights and high aspect ratios, whereas CHF3 and Ar gas plasmas resulted in nanostructures with small heights and low aspect ratios. Furthermore, it was found that the nanostructures were not covered over the entire area, and the extent to which the nanostructures were distributed varied depending on the process time. As the RIE process time increases, the nanostructure expands from the top surface of the MLA to the flat film area. This limited the light extraction efficiency improvement. At a short process time of 50 s, nanostructures were formed only on the upper surface of the MLA hemisphere, which increased the light extraction efficiency. However, at long process times over 50 s, the surface of the hemisphere of MLA was covered with vertically aligned nanostructures, which decreased the efficiency. While the flat film area was covered with nanostructures at the longest process time of ~3200 s, it was effective, but the total efficiency was further decreased by the trade-off between them. As a result, the high-aspect-ratio nanostructured MLA patterned only on the top surface of the hemispherical MLA with a 50 s O2 plasma treatment showed the highest efficiency, which was slightly higher than that of the bare MLA. We expect that if the nanostructures can be formed in a direction perpendicular to the MLA surface and the flat film area simultaneously, the light extraction efficiency would be further improved.

Quantum dots (QDs) have tremendous potential for next-generation displays due to their high color purity, photoluminescence efficiency, and power efficiency. In this work, we present a simple and cost-effective method for fabricating flexible single- and multiple-layer films, and they can be detached and attached to the outside of OLEDs as a light-scattering and color-conversion layer. Light extraction efficiency is enhanced by forming low-density structures by using the reactive ion etching (RIE) process. As a result, the QD/PDMS composite film allowed for color conversion and achieved an excellent light extraction efficiency of up to 9.2%. Furthermore, the QD/PDMS composite film and greenish-blue OLED produced white light (CIEx,y = 0.28, 0.41), demonstrating the potential for application in broad areas, from flexible displays to lighting. The method provides a simple and cost-effective alternative to conventional processes.

Blue thermally activated delayed fluorescence (TADF) top-emitting organic light-emitting diodes (TEOLEDs) have garnered widespread interest because of their 100% internal quantum efficiency (eta int) and high intensity due to microcavity effects. However, their external quantum efficiency (eta ext) is limited by total internal reflection from the thin-film encapsulation (TFE) required by TEOLEDs and their susceptibility to moisture and oxygen. This paper introduces a novel approach in which TiO2 nanoparticles (NPs) are incorporated into a negative photoresist, and Al2O3 is applied to form a nanolaminated TFE layer. This TFE layer decreases the water vapor transmission rate (WVTR), enhances light extraction efficiency and viewing angle characteristics. Moreover, the optical property can be modulated by adjusting the TiO2 NP content and a planarization layer, maintaining a total transmittance of approximately 70%. The barrier properties assessed via electrical Ca tests show that TFE achieves WVTRs below 10-5 g m-2 day-1 under ambient conditions. When applied to blue TADF TEOLEDs, the TFE improves electroluminescence by 23.78% and external quantum efficiency by 32.31%. As the viewing angle shifts from 0 degrees to 45 degrees, the CIE coordinate and peak wavelength shifts decrease from 0.067 to 0.044 and 14 to 8 nm, respectively. These results can be theoretically explained based on Mie scattering efficiency and Snell's law, as analyzed by finite-difference time-domain simulations.

This study introduces an organic light-emitting diode (OLED) light extraction method using a wavy-patterned polydimethylsiloxane (PDMS) substrate created via oxygen (O2) plasma treatment. A rapid fabrication process adjusted the flow, pressure, duration, and power of the O2 plasma treatment to replicate the desired wavy structure. This method allowed the treated samples to maintain over 90% total transmittance and enabled controlled haze adjustments from 10% to 70%. Finite-difference time-domain (FDTD) simulations were employed to determine optimal amplitudes and periods for the wavy structure to maximize optical performance. Further experiments demonstrated that bottom-emitting green fluorescent OLEDs constructed on these substrates achieved an external quantum efficiency (EQE) of 3.5%, representing a 97% improvement compared to planar PDMS OLEDs. Additionally, color purity variation was minimized to 0.044, and the peak wavelength shift was limited to 10 nm, ensuring consistent color purity and intensity even at wide viewing angles. This study demonstrates the potential of this cost-effective and efficient method in advancing high-quality display.

We selectively improved the viewing angle characteristics and light extraction efficiency of blue thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs) by tailoring a nanofiber-shaped Si3N4 layer, which was used as an internal scattering layer. The diameter of the polymer nanofibers changed according to the mass ratio of polyacrylonitrile (PAN) and poly(methyl methacrylate) (PMMA) in the polymer solution for electrospinning. The Si3N4 nanofiber (SNF) structure was fabricated by etching an Si3N4 film using the PAN/PMMA nanofiber as a mask, making it easier to adjust parameters, such as the diameter, open ratio, and height, even though the SNF structure was randomly shaped. The SNF structures exhibited lower transmittance and higher haze with increasing diameter, showing little correlation with their height. However, all the structures demonstrated a total transmittance of over 80%. Finally, by applying the SNF structures to the blue TADF OLEDs, the external quantum efficiency was increased by 15.6%. In addition, the current and power efficiencies were enhanced by 23.0% and 25.6%, respectively. The internal light-extracting SNF structure also exhibited a synergistic effect with the external light-extracting structure. Furthermore, when the viewing angle changed from 0 degrees to 60 degrees, the peak wavelength and CIE coordinate shift decreased from 20 to 6 nm and from 0.0561 to 0.0243, respectively. These trends were explained by the application of Snell's law to the light path and were ultimately validated through finite-difference time-domain simulations.

Investigated nano‐pillar‐based light extraction methods for OLEDs. Explored photosensitive photopolymer (SU‐8) based random nanostructure's impact on light extraction efficiency. Achieved 85% visible spectrum transmittance, highest efficiency with minimal unetched structure thickness. Compared to OLEDs lacking nano‐pillar structure, saw up to 38% improved quantum efficiency and 40% enhanced power efficiency. Insights aid in optimizing these structures for OLED advancement.

Luminous efficiency is a pivotal factor for assessing the performance of optoelectronic devices, wherein light loss caused by diverse factors is harvested and converted into the radiative mode. In this study, we demonstrate a nanoscale vacuum photonic crystal layer (nVPCL) for light extraction enhancement. A corrugated semi-transparent electrode incorporating a periodic hollow-structure array was designed through a simulation that utilizes finite-difference time-domain computational analysis. The corrugated profile, stemming from the periodic hollow structure, was fabricated using laser interference lithography, which allows the precise engineering of various geometrical parameters by controlling the process conditions. The semi-transparent electrode consisted of a 15 nm thick Ag film, which acted as the exit mirror and induced microcavity resonance. When applied to a conventional green organic light-emitting diode (OLED) structure, the optimized nVPCL-integrated device demonstrated a 21.5% enhancement in external quantum efficiency compared to the reference device. Further, the full width at half maximum exhibited a 27.5% reduction compared to that of the reference device, demonstrating improved color purity. This study presents a novel approach by applying a hybrid thin film electrode design to optoelectronic devices to enhance optical efficiency and color purity.

In this study, the periodic nanostructures of various shapes were fabricated using a low‐cost, low‐power continuous wave laser. The nanostructures can be easily fabricated with a low‐cost and simple process using a laser interference lithography technology. In addition, we demonstrated that various shapes such as spherical, hemispherical, and wavy can be easily controlled by adjusting the surface energy of the substrate and process parameters.

This study demonstrated organic light-emitting diodes (OLEDs) with high optical efficiency and suppressed roll-off characteristics by harvesting the synergistic effect of hybridizing the mixed-host material combination and the nanopatterning structural technique. This pioneering demonstration of nanoarray configuration in a third-generation emitting organic molecule-based device is expected to provide new strategies for the design of high-performance OLEDs.

This study investigates the application of scattering structures to the metal layer in a DMD (Dielectric/Metal/Dielectric) configuration through plasma treatment. The purpose is to enhance the light extraction efficiency of organic light-emitting diodes (OLEDs). Different plasma conditions were explored to create scattering structures on the metal layer. The fabricated devices were characterized for their electrical and optical properties. The results demonstrate that the introduction of scattering structures through plasma treatment effectively improves the light extraction efficiency of OLEDs. Specifically, using O2-plasma treatment on the metal layer resulted in significant enhancements in the total transmittance, haze, and figure of merit. These findings suggest that incorporating scattering structures within the DMD configuration can effectively promote light extraction in OLEDs, leading to enhanced overall performance and light efficiency.

In this study, various diffusers are applied to highly efficient ultra-thin emission layer (EML) structure-based blue phosphorescent organic light-emitting diodes (PHOLEDs) to improve the electroluminescence (EL) characteristics and viewing angle. To achieve highly efficient blue PHOLEDs, the EL characteristics of ultra-thin EML PHOLEDs with the various diffusers having different structures of pattern–shape (hemisphere/sphere), size (4~75 μm), distribution (surface/embedded), and packing (close-packed/random) were systematically analyzed. The diffusers showed different enhancements in the overall EL characteristics of efficiencies, viewing angle, and others. The EL characteristics showed apparent dependency on their structure. The external quantum efficiency (EQE) was enhanced mainly by following the orders of pattern, size, and shape. Following the pattern size, the EQE enhancement gradually increased; the largest-sized diffuser with a 75 μm closed-packed hemisphere (diffuser-1) showed a 1.47-fold EQE improvement, which was the highest. Meanwhile, the diffuser with a ~7 μm random embedded sphere with a low density (diffuser 5) showed the lowest 1.02-fold-improved EQE. The reference device with ultra-thin EML structure-based blue PHOLEDs showed a maximum EQE of 16.6%, and the device with diffuser 1 achieved a maximum EQE of 24.3% with a 5.1% wider viewing angle compared to the reference device without a diffuser. For the in-depth analysis, the viewing angle profile of the ultra-thin EML PHOLED device and fluorescent green OLEDs were compared. As a result, the efficiency enhancement characteristics of the diffusers show a difference in the viewing angle profile. Finally, the application of the diffuser successfully demonstrated that the EL efficiency and viewing angle could be selectively improved. Additionally, we found that it was possible to realize a wide viewing angle and achieve considerable EQE enhancement by further investigations using high-density and large-sized embedded structures of light-extraction film.

Thermally activated delayed fluorescence (TADF) organic molecules are considered the most suitable for blue organic light‐emitting diodes (OLEDs) after extensive research; however, they are plagued by issues of internally guided light and the roll‐off characteristics contributed by triplet exciton‐utilized emission. Thus, this study leverages exciton diffusion guidance and energy extraction to simultaneously achieve optical efficiency enhancement and roll‐off characteristic suppression of mixed‐host blue TADF OLEDs. The array of nanopixels, defined by the inserted nanoscale pixel‐defining layer (nPDL), spatially separates the excitons and polarons, resulting in the exacerbation of triplet quenching by securing exciton diffusion. Furthermore, through the formation of a metal cathode with a corrugated profile, nonradiative energy transfer to the surface plasmon polaritons is capitalized via Bragg diffraction, thereby boosting the emission efficiency. The structure of the nPDL is judiciously determined by finite‐difference time‐domain computational analysis. Consequently, the device with the optimized nPDL demonstrates 88.4%, 118.8%, and 108.8% improvements in external quantum, current, and power efficiencies, respectively, compared to the reference. Moreover, the critical luminance, which quantifies the degree of roll‐off, is improved by 83.7%. This pioneering demonstration of hybridizing the material combination and nanopatterning techniques is expected to provide new insights for designing high‐performance OLEDs.

In this study, we report OLEDs with improved light‐extraction efficiency by applying random nanopillar light‐extraction structures (rNPLES). OLEDs containing low‐temperature mask‐ free process‐based light‐extraction enhancement structures improved by 1.16‐fold depending on plane ratio with non‐ patterned initial polymer thickness. OLEDs with optimal rNPLES also showed a 129% improvement in external quantum efficiency and a 132% improvement in power efficiency.

This study presents an in-depth investigation of nano-pillar-based external light extraction techniques, focusing on the analysis of light extraction characteristics based on the pillar and plane structures. The nano-pillar-based external light extraction structure is formed by a process technology that allows for the formation and control of the plane thickness. In this study, a random nanostructure layer based on SU-8 was fabricated, and the impact of variations in the overall height and plane height on the light extraction efficiency of the organic light-emitting diode (OLED) was analyzed. The nanostructure layer was easily formed using a low-temperature mask-free process, enabling control of diffraction and scattering effects in the visible wavelength range. The research results demonstrate that the fabricated nanostructure layer exhibited a total transmittance of over 85% in the visible spectrum, with higher light extraction efficiency observed as the thickness of the plane structure approached zero. Furthermore, compared to OLEDs without the random nano-pillar structure (RNPS), the external quantum efficiency and power efficiency were improved by up to 37.5% and 40.4%, respectively. These findings provide valuable insights into the design and optimization strategies for random nano-pillar-based external light extraction structures, contributing to the advancement of OLED technology. This study presents an in-depth investigation of nano-pillar-based external light extraction techniques, focusing on the analysis of light extraction characteristics based on the pillar and plane structures.

In this study, we demonstrated organic light-emitting diodes (OLEDs) outcoupling with a flexible polydimethylsiloxane (PDMS) film with a micro-convex structure using the breath figure (BF) method. We can easily control the micro-convex pattern by adjusting the concentration of polystyrene and the humidity during the BF process. As process conditions to fabricate the micro-convex structure, polymer concentrations of 10, 20, 40, and 80 mg/mL and 60, 70, and 80% relative humidity were used. To evaluate the optical properties, we analyzed the transmission, diffusion, and electroluminescence with or without the micro-convex structure on the OLEDs. The shape and density of the micro-convex structure are related to its optical properties and outcoupling and we have experimentally demonstrated this. By applying a micro-convex structure, it achieved up to a 42% improvement in the external quantum efficiency compared to bare OLEDs (without any light extraction film). We expect the fabricated flexible light extraction film to be effective for outcoupling and applicable to flexible devices.