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Organic light-emitting diode (OLED) microdisplays have attracted much attention as displays for small form factor augmented reality (AR) devices. To realize glass-like thin and wide field of view (FoV) AR devices, we designed a display module with a high aspect ratio microdisplay and a thin optical component. For the high aspect ratio microdisplay, we developed the color OLED microdisplay with a 32:9 aspect ratio and a 0.8-inch diagonal ∼2,490-ppi CMOS backplane. To express color and reduce optical crosstalk, we fabricated the color filter (C/F) patterning directly on the white OLED. We also developed a pin mirror lens with 11 pin mirrors to improve the optical efficiency and quality with a thin lens. By combining the microdisplay with LetinAR’s pin mirror lens, we successfully demonstrated an AR device with a wide horizontal FoV of 46° but with a small form factor 4 mm lens.

From the very first time that graphene was used as a transparent electrode for OLED applications, the emergence of active-matrix (AM)-graphene OLED displays has been envisioned. Realizing this expectation, however, turned out to be difficult. Two obstacles are the growth and transfer of a large-area graphene film and the patterning of a graphene film into pixels. To solve these problems, a process of patterning a graphene film without surface contamination was developed. The fabrication of OLED panels by the patterned graphene anode on Gen 2(370 × 470 mm)-sized and flexible substrates was successfully demonstrated. In this work, oxide TFT arrays were combined as a switching backplane, and a pixelated graphene OLED was used as an emissive layer, to realize AM-graphene OLED displays. To explore the technical feasibility of flexible AM-graphene OLED displays, the aforementioned components were formed on a flexible substrate. For commercial-level production, all the processes that were used were chosen to be compatible with the conventional display processes.

Microdisplay is a key technology for realizing augmented reality (AR) and mixed reality (MR) devices, which have attracted much attention of late. Even though the operating voltage in the tandem structure is higher than that in the single structure, 2-stack tandem OLED exhibited 20,000 cd/m2 at 9 V, which is compatible with CMOS circuit driving. Due to its top-emitting geometry with a tandem structure, the OLED device with a well-controlled thickness exhibited a white spectrum with (0.26, 0.26) color coordinates. The pixel density of the fabricated microdisplay panel with a white tandem OLED was about 2350 pixels per inch, and the active area of the panel was 0.7 inch diagonally. The resolution of the panel was 1280 × 1024, corresponding to SXGA, and the maximal luminance was 3,000 cd/m2.

Air pollution sensors based on organic transistors have attracted much interest recently; however, the devices suffer from low responsivity and slow response and recovery rates for gas analytes. These shortcomings are attributed to the low charge-carrier mobility of organic semiconductors and to a structural limitation resulting from the use of a thick and continuous active layer. In the present work, we investigated the material properties of a multiscale porous zeolitic imidazolate framework, [Zn(2-methylimidazole)2]n (ZIF-8), and examined its potential as an analyte channel material inserted at an organic-transistor active layer. A series of carbonized zeolitic imidazolate frameworks (ZIFs) were prepared by thermal conversion of ZIF-8 and also studied for comparison. The microstructures, morphologies, and optical/electrical characteristics of polythiophene/ZIF-8 hybrid films were systematically investigated. Organic-transistor-type nitrogen dioxide sensors based on the polythiophene/ZIF-8 hybrid films showed substantially improved sensing properties, including responsivity, response rate, and recovery rate. The electrical conductivity of the carbonized ZIF-8s enhanced the field-effect mobility of the organic transistors; however, the sensing performance was not improved, because of the closed pore structures resulting from the carbonization. These results provide invaluable information and useful insights into the design of transistor-type gas sensors based on organic semiconductor/metal-organic framework hybrid films.

We investigated the optical reflectance, surface roughness, and sheet resistance of aluminum (Al)/titanium nitride (TiN), titanium (Ti), and tungsten (W) layers on Si substrates, which are available in the CMOS foundry, for organic light-emitting diode (OLED) microdisplays. The devices with different metal anode layers exhibited different hole-injection properties and OLED performances, owing to the different optical and electrical properties of metal anode layers. Based on the OLED characteristics, the Al/TiN layer was selected as an anode layer for OLED microdisplays. A green monochromatic OLED microdisplay panel was designed and implemented using the 0.11-μm CMOS process. The density of pixels was ~2 351 pixels per inch and the panel's active area was 0.7 in in diagonal. The resolution of the panel was 1 280 × 3 × 1 024, corresponding to SXGA. The panel was successfully operated, and the maximal luminance was ~460 cd/m2.

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 and 30°, which led to lower enhancement (38%) of the total luminous flux compared with the luminance enhancement (64%) in the normal direction. The luminance enhancement with the MLA film also depended on the panel area, and the smaller panels showed lower luminance enhancement than the larger ones. As for the small panels, the straying light beyond the panel areas significantly affected the luminance of the panels, and over 60% luminance enhancement was observed in the normal direction for the large panels (2500 and 6084 mm2) with the MLA film while only 48 and 58% luminance enhancements were observed at the small panels (2.25 and 70 mm2).

The ability to image pressure distribution over complex three-dimensional surfaces would significantly augment the potential applications of electronic skin. However, existing methods show poor spatial and temporal fidelity due to their limited pixel density, low sensitivity, or low conformability. Here, we report an ultraflexible and transparent electroluminescent skin that autonomously displays super-resolution images of pressure distribution in real time. The device comprises a transparent pressure-sensing film with a solution-processable cellulose/nanowire nanohybrid network featuring ultrahigh sensor sensitivity (>5000 kPa−1) and a fast response time (1000 dpi) pressure imaging without the need for pixel structures. Our approach provides a new framework for visualizing accurate stimulus distribution with potential applications in skin prosthesis, robotics, and advanced human-machine interfaces., Electronic skin that spatially maps pressure distribution through imaging shows limited performance despite improvements to data acquisition. Here, the authors report ultraflexible, transparent electroluminescent skin capable of high-resolution imaging of pressure distribution over 3D surfaces.

This chapter delineates the technical issues and integration scheme related to the use of graphene as a transparent electrode in organic light–emitting diode (OLED) applications. We address fundamental issues related to the use of graphene electrode in OLED. Later, we deal with patterning of graphene films into pixels on array scale and their integration into OLED panels. In this course, we emphasize the importance of strong adhesion of graphene film to its support and geometrically correct patterning. Finally, we demonstrate a fully operational two-color OLED module and a flexible OLED module. Our results signify the technical possibility of using graphene films as actual components in commercial OLED products.

A new structure for a switchable mirror device based on reversible electrodeposition is proposed. This device does not contain Cu ions in the electrolyte and adapts a counter electrode. The feasibility of the device was evaluated with a WO3 film, which is a well-known electrochromic material, as a counter electrode. Even in the absence of Cu ions, the WO3 film facilitates a clean erase feature in the device. Furthermore, using a pre-deposited Ag film as a working electrode, Ag deposition can be driven at a substantially lower voltage than that in conventional devices. Moreover the deposition current decreases with the progress of Ag deposition, and stops after completion of the deposition process. The results clearly indicate that the tri-bromine ion, which makes the self-erasing circulation, is not generated during Ag deposition process. The new switchable mirror shows excellent bistability and size scale-up is possible because it does not consume continuous current in the mirror state. By appling the proposed technology, a switchable mirror device with a 7 cm × 9 cm active area was successfully fabricated.

With increasing demand for transparent conducting electrodes, graphene has attracted considerable attention, owing to its high electrical conductivity, high transmittance, low reflectance, flexibility, and tunable work function. Two faces of single-layer graphene are indistinguishable in its nature, and this idea has not been doubted even in multilayered graphene (MLG) because it is difficult to separately characterize the front (first-born) and the rear face (last-born) of MLG by using conventional analysis tools, such as Raman and ultraviolet spectroscopy, scanning probe microscopy, and sheet resistance. In this paper, we report the striking difference of the emission pattern and performance of transparent organic light-emitting diodes (OLEDs) depending on the adopted face of MLG and show the resolved chemical and physical states of both faces by using depth-selected absorption spectroscopy. Our results strongly support that the interface property between two different materials rules over the bulk property in the driving performance of OLEDs.

Organic wrinkle structures are investigated as an internal scattering layer for the fabrication of highly efficient organic light-emitting diodes (OLEDs). The solution-processed wrinkle structures are planarized with a high-index layer, resulting in a reduced surface roughness and optical haze simultaneously. The OLED device including the wrinkle structures achieved external quantum efficiency (EQE) of 24.2%, corresponding to a 1.24 time enhancement with respect to that of a control device having no internal scattering layer. By attaching a micro lens array (MLA) or a half ball lens (HBL) on the external surface of the substrate, the proposed device exhibits an EQE of 30.5% (1.56 time enhancement) and 41.8% (2.14 time enhancement), respectively. Randomness of the distributed wrinkle structures is shown to provide additional benefits of reduced angular spectral distortion and Lambertian-like emission properties. Trans-scale optical simulation combining wave-optics and the geometrical effect are used for the quantitative analysis of the emission characteristics of the device.

To realize transparent organic light-emitting diodes (OLEDs), a top electrode should have excellent optical, electrical, and mechanical properties. Conventionally, transparent conductive oxides and semitransparent metal have been widely used for transparent top electrodes, but they have several fundamental drawbacks. We herein report efficient large-area inverted transparent OLEDs using a vacuum-laminated top electrode with an embedded metal mesh. The laminated device with 1 mm pitch exhibits superior optical properties including a high transmittance of 75.9% at 550 nm, a low reflectance of 12.0% at 550 nm, and spectrally flat characteristics over the entire visible region and shows nearly ideal Lambertian angular emission characteristics with little angular color shift in both directions. Moreover, the lowered sheet resistance of 4 Ω/sq originating from the embedded metal mesh (1 mm pitch) led to efficient and uniform emission characteristics. As a result, the device shows a relatively high maximum curre...

We have developed down-conversion outcoupling films to enhance the light outcoupling efficiency in white organic light-emitting diodes (OLEDs). The down-conversion outcoupling films consist of outcoupling structures and color conversion materials, which are prepared by a simple solution-based micro-imprint process and are adopted into OLEDs. The down-conversion films successfully realize white light by converting blue rays from blue phosphorescent OLED. The OLEDs based on the down-conversion films with outcoupling structures show a great improvement of power efficiency by a factor of 1.32 compared to the reference OLED based on down-conversion films without outcoupling structures. Furthermore, the influence of a concentration of color conversion materials on color rendering index of OLEDs is investigated. The results strongly indicate that readily fabricated down-conversion light outcoupling films by a simple micro-imprint process are highly promising for enhanced light extraction performance and high color rendering index of white OLEDs.

As potential lighting-emitting devices, electrochemiluminescence (ECL) devices are promising in terms of device structure and fabrication and involve low processing cost compared to organic light-emitting devices (OLEDs). Herein, liquid electrolyte-based multi-colored ECL devices (ECLDs) were prepared with organic materials dissolved in electrolyte solution, which generated red, yellow, green, and blue emissions under an applied square-wave AC bias voltage. Among the four different emissive colors, yellow showed a strong and stable emission, which enabled quantitative measurements, including a luminance of 12 cd m−2 at 4.5 V.

In this paper, a new light-adaptable display (LAD) structure with minimum power consumption is proposed for the future advertising service, and the demonstrated results are reported. An organic light-emitting diode with color reflection (colored OLED) was applied for the reflective- and emissive-mode device, and a guest-host liquid-crystal device (GH-LC) was adopted for the light shutter device. The current efficiency and reflectance of the colored OLED were 35.15 cd/A at 457 cd/m2 luminance and 63% for the yellow color, respectively. The measured contrast ratio of GH-LC was 15.5:1 at dark-room conditions, respectively. Transparent oxide thin-film transistors were used for the backplane, and their average mobility was 9.08 cm2/V s, with a 0.5 standard deviation. Through the optimization of the fabrication process and the structures of each device, the LAD adaptively operating according to the environmental illuminance from dark to 10,000 nits was successfully demonstrated. Moreover, a new LAD driv...

A switchable diffraction device capable of driving with segment electrodes has been proposed and its operating characteristics were analyzed. The switchable diffraction device is based on a variable cavity structure using reversible electrodeposition technology and two kinds of diffraction gratings are designed to be selectively switched according to the driving electrode. The fabricated device was able to switch the diffraction patterns without any interference between the electrodes, which means that the interference between the electrodes will not be a problem in further device integration with driving circuits. However, when the electrode isolation is not perfect due to parasitic resistance between the electrodes, a weak interference between the electrodes is observed in the diffraction pattern. Therefore, it is expected that ensuring complete insulation between the electrodes will be a very important in the integration of the device. The proposed device can be used as a light control device, an image switchable hologram, etc. Furthermore, it is expected to be applied to reconfigurable metasurfaces through integration with active matrix circuits in the future.

Highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) ( Pedot PSS) films as transparent electrodes for organic light-emitting diodes (OLEDs) are doped with a new solvent 1,3-dimethyl-2-imidazolidinone (DMI) and are optimized using solvent post-treatment. The DMI doped Pedot PSS films show significantly enhanced conductivities up to 812.1 S cm(-1) . The sheet resistance of the Pedot PSS films doped with DMI is further reduced by various solvent post-treatment. The effect of solvent post-treatment on DMI doped Pedot PSS films is investigated and is shown to reduce insulating PSS in the conductive films. The solvent posttreated Pedot PSS films are successfully employed as transparent electrodes in white OLEDs. It is shown that the efficiency of OLEDs with the optimized DMI doped Pedot PSS films is higher than that of reference OLEDs doped with a conventional solvent (ethylene glycol). The results present that the optimized Pedot PSS films with the new solvent of DMI can be a promising transparent electrode for low-cost, efficient ITO-free white OLEDs.

To improve a viewing angle characteristic as well as a light extraction effect, we fabricated nanoporous polymer film (NPF) as a scattering medium as well as a light extraction component. We designed two types of organic light emitting diodes (OLEDs) with strong microcavity effect containing two different hole transport layer (HTL) thickness (e.g. 30 nm and 60 nm) to investigate each optical behavior of NPF. Very interestingly, we could observe a significant enhancement of external quantum efficiency (EQE) for each device [30 nm thick HTL : 18.0 %, 60nm thick HTL : 31.6 %] when we attached 125 um thick PET film coated with NPF. Furthermore, NPF successfully suppress the viewing angle dependence to realize ideal angular emission even though it's somehow different from that of Lambertian distribution.

We have fabricated transparent inverted organic light-emitting diodes (OLEDs) using a metal mesh embedded conductive film (MEF) with a non-metal transparent conductor and a novel vacuum lamination method. The device with the proposed electrode exhibits higher transmittance, lower reflectance, and especially much more stable optical properties than those of the conventional OLEDs with thin metal top electrodes over an entire visible region. Moreover, lower driving voltage is also achieved due to the embedded metal mesh. We demonstrate its potential as a reliable transparent top electrode in various optoelectronic devices.

We report on highly efficient blue, orange, and white phosphorescent organic light emitting diodes (PHOLEDs) comprising of only two organic layers. Hole transporting 4,4’,4’’-tris(N-carbazolyl)triphenylamine (TcTa) and electron transporting 2-(diphenylphosphoryl) spirofluorene (SPPO1) were used as an emitting host for orange light-emitting bis(3-benzothiazol-2-yl-9-ethyl-9Hcarbazolato) (acetoacetonate) iridium ((btc)2(acac)Ir) and blue light-emitting iridium(III)bis(4,6-difluorophenylpyridinato-N,C2’) picolinate (FIrpic) dopant, respectively. Combining these two orange and blue light-emitting layers, we successfully demonstrated a highly efficient white PHOLEDs with maintaining Commission Internationale de L’Eclairage (CIE) coordinates of (x = 0.373, y = 0.443). Accordingly, we achieved a maximum external quantum, current, and power efficiencies of 12.9 %, 30.3 cd/A, and 30.0 lm/W without out-coupling enhancement.

Enhancing outcoupling efficiency and stabilizing emission spectra are of high technical importance in realizing high quality white transparent organic light emitting diodes (TOLEDs). In this work, we demonstrate a random nano-scattering layer (RSL) as a structure which can effectively address those tasks. The RSL contributes to bottom and top emissions by scattering and reflection, respectively. With the use of RSL, we achieved remarkable total efficiency enhancement of 101%. Also, a viewing angle independent stable white spectrum with a color rendering index of 79 was achieved. With its straight forward processing, our RSL can be readily applied to deal with various photonic applications to enhance both efficiency and emission spectra.

White organic light-emitting diodes (WOLEDs) are one of the most promising technologies to realize future solid-state lighting with high power efficiency, broad and adjustable spectral coverage, and area emission for more effective and natural illumination. In this work, we report a new method of tuning the correlated color temperature (CCT) of WOLEDs via spatially controlling the degree of the micro-cavity effect in an OLED. Varying the width of thin Ag strips deposited on top of a transparent electrode leads to changes in both intensity and phase of reflection at the anode, hence significantly altering emission spectra of proposed WOLEDs. CCT of the implemented WOLEDs span a wide range, from 3000 K to 8000 K, demonstrating that our proposed approach helps to meet the need for lighting with various CCTs.

Extracting the confined light is of critical significance in achieving highly energy efficient organic light emitting diodes. To address the task of extracting the confined light, we here synthesize a new type of liquid prepolymer, which spontaneously forms wrinkles upon ultra-violet light exposure. The spontaneously formed organic wrinkle is successfully applied not only in extracting the confined light but also in inducing angular spectral stability. Simulations demonstrate that the wrinkles can lower incident angle of light impinging on the substrate/air interface and thus help extract a large portion of light delivered to the substrate. In particular, it is shown that geometrical optimization of the size and aspect ratio of wrinkles is important in obtaining the highest light extraction. With the simplicity of the process and size controllability, the proposed wrinkle-based approach can be readily realized over a large area, opening up a new avenue in various photonics applications.

Modification of multilayer graphene films was investigated for a cathode of organic light-emitting diodes (OLEDs). By doping the graphene/electron transport layer (ETL) interface with Li, the driving voltage of the OLED was reduced dramatically from 24.5 to 3.2 V at a luminance of 1000 cd/m2. The external quantum efficiency was also enhanced from 3.4 to 12.9%. Surface analyses showed that the Li doping significantly lowers the lowest unoccupied molecular orbital level of the ETL, thereby reducing the electron injection barrier and facilitating electron injection from the cathode. Impedance spectroscopy analyses performed on electron-only devices (EODs) revealed the existence of distributed trap states with a well-defined activation energy, which is successfully described by the Havriliak-Negami capacitance functions and the temperature-independent frequency dispersion parameters. In particular, the graphene EOD showed a unique high-frequency feature as compared to the indium tin oxide one, which could be explained by an additional parallel capacitance element.

Recently, we have addressed that a formation mechanism of a nanolens array (NLA) fabricated by using a maskless vacuum deposition is explained as the increase in surface tension of organic molecules induced by their crystallization. Here, as another research using finite difference time domain simulations, not electric field intensities but transmitted energies of electromagnetic waves inside and outside top-emitting blue organic light-emitting diodes (TOLEDs), without and with NLAs, are obtained, to easily grasp the effect of NLA formation on the light extraction of TOLEDs. Interestingly, the calculations show that NLA acts as an efficient light extraction structure. With NLA, larger transmitted energies in the direction from emitting layer to air are observed, indicating that NLAs send more light to air otherwise trapped in the devices by reducing the losses by waveguide and absorption. This is more significant for higher refractive index of NLA. Simulation and measurement results are consistent. A successful increase in both light extraction efficiency and color stability of blue TOLEDs, rarely reported before, is accomplished by introducing the highly process-compatible NLA technology using the one-step dry process. Blue TOLEDs integrated with a N, N'-di(1-naphthyl)- N, N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine NLA with a refractive index of 1.8 show a 1.55-times-higher light extraction efficiency, compared to those without it. In addition, viewing angle characteristics are enhanced and image blurring is reduced, indicating that the manufacturer-adaptable technology satisfies the requirements of highly efficient and color-stable top-emission displays.

For environmental reason, buildings increasingly install smart windows, which can dim incoming daylight based on active electrochromic devices (ECDs). In this work, multi-layered graphene (MLG) was investigated as an ECD window electrode, to minimize carbon dioxide (CO2) emissions by decreasing the electricity consumption for building space cooling and heating and as an alternative to the transparent conductor tin-doped indium oxide (ITO) in order to decrease dependence on it. Various MLG electrodes with different numbers of graphene layers were prepared with environmentally friendly poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) to produce ECD cells. Tests demonstrated the reproducibility and uniformity in optical performance, as well as the flexibility of the ECD fabrication. With the optimized MLG electrode, the ECD cells exhibited a very fast switching response for optical changes from transparent to dark states of a few hundred msec.

Optical, interfacial and patterning issues of anode graphene films in organic light emitting diode (OLED) applications were investigated. In the optical part, the microcavities of graphene and indium tin oxide (ITO) anode OLEDs were contrasted. With the use of graphene one may avoid spectral and organic stack design problems related to microcavity problems. However, due to the weak microcavity, emission enhancement using interference designs is practically impossible. By inserting an electron acceptor insert at the graphene/hole transport layer (HTL) interface, it was possible to enhance the current density by factor of three. Based on in situ ultraviolet photoelectron spectroscopy (UPS) results, the insert was interpreted as being a charge generation layer. Graphene patterning using laser or plasma methods turned out to be problematic. None of those methods could offer acceptable dimension accuracy and preserved graphene quality.

Reported in this work is the fabrication of white transparent organic light-emitting diodes (TOLEDs) with high color rendering indices (CRIs). An architecture in which the green and red emission layers are sandwiched between two blue emissions layers was used. By tuning the thicknesses of the green and red emission layers, CRI and power efficiency values of 90/20.5 and 87/6.8 lm/W were achieved in the bottom and top emissions, respectively. The study results suggest an effective engineering approach for realizing high CRI white TOLED lighting sources.

We report on a novel fabrication method for organic lightemitting diodes (OLEDs) by using a multilayered graphene (MLG) film and a lamination technique. The OLED structure with the MLG top electrode has higher transmittance and lower reflectance than the OLED structure with the conventional thin metal electrode. Moreover, higher luminous current efficiency of the device with the MLG top electrode has been achieved compared with that of the conventional bottom-emission OLEDs with aluminum metal electrode.

Due to the very low light extraction efficiency of conventional organic light-emitting diodes (OLEDs), the application of OLEDs for next-generation lighting remains limited. Therefore, in order to enhance the light extraction efficiencies that result in improving the luminous efficacy (LE, lm W−1) and external quantum efficiency (ηEQE, %) of OLEDs, three different geometrically profiled, negatively nanostructured periodic semi-pyramid polydimethylsiloxane (PDMS) layers are used to create a hole at depths of 500 nm, 650 nm, and 1000 nm; these are designated as the polymeric lighting extraction film (PLEF) I, PLEF II, and PLEF III, respectively. These layers are placed directly on the backside of the green emissive bottom-emitting OLED (BE-OLED) glass substrates as an outcoupling enhancement PLEF that improves the glass substrate/air interface. Through the simple combination with three different nanostructures on each green emissive BE-OLED, a maximum enhancement of up to 50% is achieved in the LE and ηEQE measured at the same brightness, which is 1.5 times higher than the reference green emissive BE-OLED without a PLEF. Therefore, global energy saving can be achieved through reducing the power consumption by up to 30% possibly estimated from LE using the integrated PLEFs.

The carrier injection efficiencies of organic light-emitting diodes with a multilayer graphene (MLG) anode were compared for different hole injection layers (HIL). The energy level alignments at the hole injecting interface were also studied by using the ultraviolet photoelectron spectroscopy (UPS). We employed 1,1-bis[4-[N,N′-di(p-tolyl)amino]phenyl]cyclohexane (TAPC) as the hole transporting materials, while N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)benzidine (NPB) or 1,4,5,8,9,12-hexaaza-triphenylene-2,3,6,7,10,11-hexacarbonitrile (HAT-CN) was used as the HIL. The current–voltage characteristics of hole-only devices showed that the MLG anode was only slightly inferior to the indium-tin oxide (ITO) anode in hole injection performance for all the HIL layers. The best efficiency was observed for both MLG and ITO anodes with HAT-CN HIL. We compared UPS-measured energy level alignment of TAPC/HIL/MLG interface for different HILs and concluded that the unique charge generation interface at TAPC/HAT-CN played a crucial role for the improved performance of HAT-CN HIL.

We developed a highly refractive index planarization layer showing a very smooth surface for organic light-emitting diode (OLED) light extraction, and we successfully prepared a highly efficient white OLED device with an embossed nano-structure and highly refractive index planarization layers. White OLEDs act as an internal out-coupling layer. We used a spin-coating method and two types of TiO2 solutions for a planarization of the embossed nano-structure on a glass substrate. The first TiO2 solution was TiO2 sol, which consists of TiO2 colloidal particles in an acidic aqueous solution and several organic additives. The second solution was an organic and inorganic hybrid solution of TiO2. The surface roughness (Ra) and refractive index of the TiO2 planarization films on a flat glass were 0.4 nm and 2.0 at 550 nm, respectively. The J–V characteristics of the OLED including the embossed nano-structure and the TiO2 planarization film were almost the same as those of an OLED with a flat glass, and the luminous efficacy of the aforementioned OLED was enhanced by 34% compared to that of an OLED with a flat glass.

Semi-transparent, colored organic light-emitting diodes (OLEDs) were demonstrated by comprising a microcavity-embedded structure that uses an organic layer sandwiched between thin metal layers as the cathode. Without bias, the colored OLEDs exhibited various colors depending on the metal/organic/metal cathode configuration, by means of internal interference effects under ambient illumination. By varying the thickness of the organic layer, the transmittance and reflectance of the colored OLEDs could be controlled. The influence of the microcavity cathode on the light-emitting performances of OLEDs, such as the efficiencies and the electroluminescence spectra, was also studied.

We suggest a new approach to improve both out-coupling efficiency and spectrum independency on viewing angle in transparent OLEDs by introducing a random nano-structured scattering layer where the waveguide mode can be minimized between the glass substrate and the ITO layer. As a result, total efficiency was remarkably enhanced in transparent OLEDs and we have achieved 52.6 lm/W with CRI 80 with over 50% of transmittance using the random nano-structured scattering layer.

We report that a potassium borohydride (KBH4)-doped 1,3,5-tri(m-pyrid-3-yl-phenyl)benzene (TmPyPB) layer can be utilized as an efficient electron-injection layer (EIL) for the inverted bottom-emission organic light-emitting diodes (IBE-OLEDs). The KBH4-doped EIL in the IBE-OLEDs having tris(2-phenylpyridine)iridium(III) as a green phosphorescent dopant show a lower turn-on voltage (∼7 V) and about two times higher efficiency (∼13.9% and 44.5 cd A−1 at 0.63 mA cm−2) compared with the device without the KBH4-doped EIL. Furthermore, the KBH4-doped EIL rarely affects the electroluminescence spectrum of the device. The KBH4-doped TmPyPB films with different doping ratios are also analyzed by using electron-only devices (EODs) and X-ray photoemission spectroscopy. As the doping ratio of the KBH4 increases, the current of the EOD and the amounts of potassium increase. This result indicates that the potassium improves the electron-injection ability of an organic electron-transport layer. Therefore, the KBH4-doped EIL can be utilized as an effective EIL in the inverted structure OLEDs.

We report highly efficient all phosphorescent white organic light-emitting diodes (OLEDs) with an exciton-confinement structure. By stacking two emissive layers (EMLs) with different charge transporting properties, effective charges as well as exciton confinements were achieved. Accordingly, efficient blue OLEDs with a peak external quantum efficiency (EQE) over 22% and power efficacy (PE) over 50 lm/W were developed by using iridium(III) bis(4,6-(difluorophenyl) pyridinato-N,C2′)picolinate (FIrpic) as an electro-phosphorescent dopant. When the optimized orange and red EMLs were sandwiched between the stacked two blue EMLs, white OLEDs with an EQE and PE of 24.3% and 45.9 lm/W at a luminance of 1000 cd/m2 were obtained without the use of any out-coupling techniques. In addition, these white OLEDs exhibit a color rendering index (CRI) value of 84 with high efficacy.

A random scattering layer (RSL) consisting of a random nano-structure (RNS) and a high refractive index planarization layer (HRI PL) is suggested and demonstrated as an efficient internal light-extracting layer for transparent organic light emitting diodes (TOLEDs). By introducing the RSL, a remarkable enhancement of 40% and 46% in external quantum efficiency (EQE) and luminous efficacy (LE) was achieved without causing deterioration in the transmittance. Additionally, with the use of the RSL, the viewing angle dependency of EL spectra was reduced to a marginal degree. The results were interpreted as the stronger influence of the scattering effect over the microcavity. The RSL can be applied widely in TOLEDs as an effective light-extracting layer for extracting the waveguide mode of confined light at the indium tin oxide (ITO)/OLED stack without introducing spectral changes in TOLEDs.

In this work, we demonstrated color-tunable white organic light-emitting diodes by stacking upper orange transparent and lower blue bottom emission organic light-emitting diodes (OLEDs). By independently operating each OLED, it was possible to tune the color temperature in a range of 1500–10,000 K, which covers the full Planckian locus in the 1931 CIE space. In designing stable and efficient OLEDs, in addition to the electrical characteristics, the importance of internal microcavity was emphasized and implemented. In fabricating the upper transparent OLED, special attention was paid to the capping layer for enhancing the emission. Our results presented a general guideline that is practically useful in designing high-performance color-tunable OLEDs with transparent OLEDs.

In this study, we demonstrated a nano-structured random scattering layer (RSL) as an internal light extraction method to improve the light extraction efficiency of organic light-emitting diodes (OLEDs). Using dewetted Ag droplets as a hard mask, we textured the glass surface to have a scattering layer of the random structure. OLEDs equipped with the RSL showed more that 50% improvement in the external quantum efficiency (EQE) and luminance efficacy (LE) compared to OLEDs without the RSL. This improvement can be understood by the scattering effect which reduces the optical loss at wave-guided modes. Also, by combining the RSL and an external light extraction micro-lens array (MLA), it was possible to achieve further improvements of 105.8% and 92.06% in the EQE and the LE, respectively.

To date, all deposition equipment has been developed to produce planar films. Thus lens arrays with a lens diameter of

We investigated the control of micro-cavity (MC) effects in organic light-emitting diodes (OLEDs) with the introduction of a striped thin metal layer between the indium tin oxide (ITO) layer and the hole transporting layer (HTL). With an enhanced MC effect obtained through the inserted metal layer, the forward emission of the OLED became stronger and the angular distribution became more forward-directed, leading to a current efficiency (CE) that was nearly 1.45 times higher than that of the reference device without the inserted metal layer. The net CE of the OLEDs with a striped metal layer was found to be determined by the area-weighted average of the CE’s of full-cavity-enhanced OLEDs and non-cavity OLEDs. It was also observed that the trade-off between resonance enhancement in efficiency and angle-dependent color stability, often found problematic in MC-based OLEDs, could be mitigated in a straight-forward manner by changing the relative portion of the metal-covered area.

In this work, we develop a simulation method to predict a two-dimensional luminance distribution method using a circuitry simulation. Based on the simulation results, we successfully fabricate large area (90 mm × 90 mm) transparent organic light-emitting diode panels with high luminance uniformity.