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The enhancement of the luminance of organic light-emitting diode (OLED) panels with various areas (2.25–6084 mm²) using a microlens array (MLA) film was investigated. The luminance enhancement was dependent on the viewing angle, and the largest enhancement (64%) was observed in the normal direction while 60 and 18% enhancements were observed at 60...
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... make inroads into the general lighting market, the luminous efficiency has to be higher than that of the conventional lightings. The external quantum efficiency of OLED is limited by the wave-guiding and total inter- nal reflection in the glass substrate, as shown in Figure 1 [4,5]. Various approaches to the improvement of the light extraction from OLEDs have been adopted. ...
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... series of OLED panels were fabricated using the following configuration: glass substrate(0.7 mm)/anode (70 nm)/organic layers(220 nm)/cathode(100 nm), as shown in Figure 1. The dimensions of the fabricated OLED panels were 2.25, 70, 2500, and 6084 mm 2 . ...
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... MLA film was obtained from MIRAENAN- OTECH Co. The diameter of the microlens was 10 μm (see Figure 1), the sag was 0.5, and the refractive index was 1.5. The MLA film was attached to the glass substrate of an OLED panel using an optical adhesive whose refrac- tive index matches that of the glass. ...
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Citations
... Light extraction technologies primarily focus on minimizing light loss by reducing the refractive index mismatch within the OLED, thereby lessening total internal reflection [10,11]. Various optical structures have been integrated into OLED devices for this purpose, including microlens array (MLA) [12,13], visible parylene film [14], MLA patterned parylene substrate [15], random surfaces [16], porous cellulose paper [17], and light scattering layers [18][19][20]. Among these studies, research Molecules 2024, 29, 73 2 of 8 using parylene has produced a light extraction film that can serve as a flexible substrate and exhibits a high outcoupling efficiency exceeding 20%. ...
In this paper, we demonstrate the use of polymer dispersed liquid crystal (PDLC) imprinted with a microlens array (MLA) via solution process to improve the outcoupling efficiency of organic light emitting diodes (OLEDs). The PDLC, well known for its scattering effect, is an excellent technology for improving the outcoupling efficiency of OLEDs. Additionally, we introduce a simple spin-coating process to fabricate PDLC which is adaptable for future solution-processed OLEDs. The MLA-imprinted PDLC applied OLED shows an enhancement factor of 1.22 in outcoupling efficiency which is a 37.5% increase compared to the existing PDLC techniques without changing the electrical properties of the OLED. Through this approach, we can expect the roll-to-roll based extremely flexible OLED, and with further research on pattering PDLC by various templates, higher outcoupling efficiency is achievable through a simple UV irradiation process.
... Further, Han et al. 82 investigated enhancement of the luminance by the micro lens array (MLA) that mostly depends on the viewing angles and luminescence area and rarely depends on the driving conditions. Therefore, for the large panel's, luminescence is improved up to 64% in normal direction with the MLA film. ...
This article presents a review on various aspect of organic light emitting diodes (OLEDs), such as their working, various categorization, impact of fabrication methodologies (organic vapor phase deposition, vacuum thermal evaporation, inkjet printing etc.) that are low-cost and their applications in serval domains like medical, sensor, display, lighting etc. Three categorizations of OLED are discussed with respect to circuit, architecture and color of emission. Different layers of multi-layered structures such as injection layer, transport layer, block layers are also reviewed and their impacts are analyzed and compared. Moreover, an experimental fabrication technique for flexible substrate is reviewed that highlights low-cost fabrication method. In this technique, dynamic viscosity and contact angle are measured using rotational viscometer and contact angle meter, respectively. The result illustrates sheet resistance and effective opening ratio of 3.8 ohms per square and 82.5%, correspondingly. Additionally, various performance parameters like luminescence, external quantum efficiency, and current efficiency are compared. The paper also incorporates recent advancement in organic thin film transistors along with some OTFT driven OLED devices.
... As the temperature increases (298-523 K), the emission intensity drops slowly as the full width at half maximum (FWHM) results increase (97-103 nm). With the structural coordinate setting as well as the Boltzmann allocation, the reliance on temperature for FWHM in the discharge of Ce 3+ may be represented as [9]. ...
span>For the task of realizing greater progress for the light output in white light-emitting diodes (WLEDs), t his study focuses on the luminescence temperature subordination feature of CaSc<sub>2</sub>O<sub>4</sub>:Ce<sup>3+</sup> phosphor (abbreviated to CaS for this study). Some other aspects of the phosphor were also included in this piece of paper: Huang-Rhys coupling factor, Stokes shift, triggering power, abatement temperature and especially, abatement behavior in CaSc<sub>2</sub>O<sub>4</sub>:Ce<sup>3+</sup>. Creating the bluish-green LEDs by the combination of blue InGaN chip and CaSc<sub>2</sub>O<sub>4</sub>:Ce<sup>3+</sup> is the primary purpose. CaSc<sub>2</sub>O<sub>4</sub>:Ce<sup>3+</sup> appears to be a decent green phosphor that can be used in WLEDs made of blue InGaN chip. Production tasks may be based on our investigation for the task of making desirable WLED devices that meet the production demands.</span
... In other recent developments, Han et al [36] addressed the effect of the MLA outcoupling enhancement on large area emitters (up to 6084 mm 2 ). In addition to the area, they also evaluated the viewing angle effects. ...
OLED technology continues to make strides, particularly in display technology with costs decreasing and consumer demand growing. Advances are also seen in OLED solid state lighting (SSL), though broad utilization of this technology is lagging. This situation has prompted extensive R&D to achieve high efficiency SSL devices at cost-effective fabrication. Here we review advances and challenges in enhancing forward light outcoupling from OLEDs. Light outcoupling from conventional bottom (through the transparent anode)-emitting OLEDs is typically ~20%, due largely to losses to external, i.e., substrate waveguide modes, internal waveguide modes between the metal cathode and the anode/substrate interface, and surface plasmon-polariton modes at the metal cathode/organic interface. We address these major photon loss paths, presenting various extraction approaches. Some approaches are devoid of light extraction structures; they include replacing the commonly used ITO anode, manipulating the refractive index of the substrate and/or organic layers, and evaluating emitters with preferential horizontal transition dipoles. Other approaches include the use of enhancing structures such as microlens arrays, scattering layers, patterned substrates, as well as substrates with various buried structures that are planarized by high index layers. A maximal external quantum efficiency as high as 78% was reported for white planarized OLEDs with a hemispherical lens to extract the substrate mode. Light outcoupling from OLEDs on flexible substrates is also addressed, as the latter become of increasing interest for foldable displays and decorative lighting, with plastic substrates being evaluated also for biomedical, wearable, and automotive applications.
... The MLA structure decreases the light angle through refraction, reducing the loss at the interface and improving the light extraction. Namely, more light is extracted out due to interface morphology changed by the MLAs [20]. Figure 9 shows the luminescence properties of OLEDs attached with MLAs replicated from the improved MLA templates and compared with those of the reference ones without MLAs. ...
In this paper, microlens array (MLA) templates with high filling factors were prepared by combining a thermal reflow method and parylene chemical vapor deposition (CVD). Then photoresist MLAs were replicated from the MLA templates by using ultraviolet nanoimprint technology. The surface morphology of the replicated photoresist MLAs was characterized by scanning an electron microscope and optical microscope. Results show that the photoresist MLAs have a relatively smooth surface, and the filling factor has been improved obviously. Also, the surface profiles of the MLAs were measured. The optical imaging properties of the MLAs were also characterized, and they had a relatively good imaging performance. Finally, the photoresist MLAs were applied on organic LEDs (OLEDs), and their luminance and current efficiencies were measured. Results show that the current efficiency of the OLEDs increased by about 42.41%, 29.01%, and 35.51%, respectively, for OLEDs with circular, hexagonal, and square MLAs. All the results above indicate that it is a simple and effective process to prepare MLA templates with high filling factors by combining thermal reflow and CVD techniques, and the prepared photoresist MLAs have great application potential in OLED areas.
... One major limiting factor in organic light emitting devices resides in the light loss due to waveguide and surface plasmon modes [108] and for which several solutions have been proposed including planar microcavities [109], lens sheets [110], photonic crystals [111], index-engineered substrates [112]. Fabricating cavities in organic thin film devices [113] is not always compatible with device structure and integration in more complex architectures. ...
Organic light emitting transistors (OLETs) represent a relatively new technology platform in the field of optoelectronics. An OLET is a device with a two-fold functionality since it behaves as a thin-film transistor and at the same time can generate light under appropriate bias conditions. This Review focuses mainly on one of the building blocks of such device, namely the gate dielectrics, and how it is possible to engineer it to improve device properties and performances. While many findings on gate dielectrics can be easily applied to organic light emitting transistors, we here concentrate on how this layer can be exploited and engineered as an active tool for light manipulation in this novel class of optoelectronic devices.
... To obtain high performance OLEDs, it is prerequisite to improve the light extraction efficiency of the device. Many research groups have developed external light extractors such as micro-lens array (MLA) [4][5][6][7], cylindrical geometry substrate [8], high refractive index (HRI) substrate [9][10][11] and external/ internal light scattering layer [12][13][14][15]. Specifically, the insertion of a light scattering layer comprised of HRI nanoparticles (NPs) into substrate has attracted immense attention because it could fine-tune the refractive index of the substrate and promotes the light out-coupling from both substrate and ITO/organic interface. ...
Organic light-emitting diodes (OLEDs) are widely commercialized in the display market due to many advantages such as wide color gamut, outstanding flexibility, and high contrast ratio. However, the performance of OLED is often hindered by the refractive index differences between the anode, substrate, and air, leading to inefficient light out-coupling from the device. In this study, we designed a polymer substrate incorporated with barium titanium oxide (BaTiO 3) nanoparticles (NPs) with high refractive index to function as a bifunc-tional scattering substrate for efficiency enhancement of OLEDs. Fine-tuning the concentration of BaTiO 3 NPs enables direct control of the refractive index and optical scattering of the substrate. The results show that the luminance efficiency and external quantum efficiency of OLED employing BaTiO 3 embedded substrate are approximately 1.6 times higher than its pristine counterpart. Evidently, the nanocomposite polymer substrate demonstrated herein could serve as an efficient light out-coupling medium for flexible OLEDs.
... Therefore, outcoupling enhancement technologies for overcoming the short lifetime by operating at a low current density have been extensively investigated. These investigations have included suppressing the TIR and, in turn, easily increasing the efficiency by attaching or forming microlens arrays (MLAs) on the substrate surface [14][15][16][17][18]. However, this technology results in blurry pixel problems, where the distinction of pixel boundaries via visual inspection is impossible, thereby preventing its use in commercialized display applications [19,20]. ...
The current efficiency and color purity of organic light-emitting diodes (OLEDs) can be easily improved by means of a microcavity structure, but this improvement is typically accompanied by a deterioration in the characteristics of viewing angle. To minimize the angular dependence of the color characteristics exhibited by these strong microcavity devices, we investigated the changes in the optical properties of the green OLED with a bottom resonant structure. This investigation was based on varying the hole transport layer and semitransparent anode thicknesses. The results of optical simulations revealed that the current efficiency and viewing angle characteristics can be simultaneously improved by adjusting the thickness of the two layers. Furthermore, optical simulations predicted that the angular color dependence could be limited to 0.019 in the International Commission on Illumination (CIE) 1976 coordinate system. This optimum condition yielded a current efficiency of ∼134 cd/A. To further reduce this color shift, a nanosized island array (NIA) was introduced through the dewetting process of cesium chloride. By employing NIAs, the color coordinate shift value was reduced to 0.016 in the CIE 1976 coordinate system, and a current efficiency of 130.7 cd/A was achieved.
... Therefore, an effective light management strategy is required in order to avoid efficiency drop due to internal light loss [7][8][9]. Several methods which include application of porous nanocellulose [10], micro-lens arrays (MLA) [11][12][13][14], MLA-patterned substrates [15], or introduction of photonic crystal layers [16] and light-scattering layers [17,18], have been developed for both external and internal light extraction purposes. Among them, the method involving external scattering layers is regarded most practical as they can be made with relatively simple methods and applied with little interference with the established device structure and process. ...
Random Al2O3 nanoparticle-based polymer composite films are investigated as external scattering layers to enhance light extraction from flexible organic light-emitting diodes (OLEDs). We found that the size and concentration of the nanoparticles (NPs) in the polymer film play a crucial role in improving light extraction. It turned out that their increase has a favorable impact on the light output of the devices, as the high concentration of the NPs leads to the formation of large nanoparticle clusters, which, in turn, yield pore-containing films. As a result, light extraction efficiency of the flexible OLEDs on PEN substrates was enhanced by a factor of 1.65 by the incorporation of the scattering layer, with the highest Al2O3 NP concentration of 99 wt%. This outcome is attributed to the reduction of the waveguide mode and total internal reflection at the substrate/air interface induced by the randomly distributed NPs in the flexible scattering layer. Our work demonstrates an efficient, solution-processable, and low-cost light-outcoupling structure for large-area and flexible OLED applications.
... 1) Many methods have been developed to enhance light extraction efficiency and high external quantum efficiencies have been demonstrated. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] However, the technologies are not compatible with current OLED manufacturing processes. Using rigid, glass-based top-emitting OLEDs (TOLEDs), we have recently demonstrated enhancements of light extraction efficiency and good color stability achieved by N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′diamine (NPB) nano-lens arrays (NLAs; lens size <1 μm) formed on top of an indium zinc oxide (IZO) top electrode. ...
