High‐performance white OLEDs with high color‐rendering index for next‐generation solid‐state lighting

Abstract— Several white‐OLED structures with a high color‐rendering index (CRI) were investigated for lighting applications. A two‐unit fluorescent/phosphorescent hybrid white OLED achieved an excellent CRI of 95, high luminous efficacy of 37 lm/W, and long lifetime of over 40,000 hours at 1000 cd/m². White‐OLED lighting panels of 8 × 8 cm for high‐luminance operation were fabricated, and a stable emission at 3000 cd/m² was confirmed. Quite a small variation in chromaticity in a different directions was achieved by using an optimized optical device structure. With a light‐outcoupling substrate, a higher efficacy of 56 lm/W, high CRI of 91, and longer half‐decay lifetime of over 150,000 hours at 1000 cd/m² was achieved. All‐phosphorescent white OLEDs placed on the light‐outcoupling substrate show a high CRI of 85 and higher efficacy of 65 lm/W with a fairly good half‐decay lifetime of over 30,000 hours. With a further voltage reduction and a high‐index spherical extractor, 128 lm/W at 1000 cd/m² has been achieved.     

Highly efficient white organic light‐emitting diodes with over 100 lm/W for next‐generation solid‐state lighting

High‐performance two‐unit all‐phosphorescent white devices on a built‐up light extraction substrate that comprised high‐index materials were studied. As a result of suitable optical and electrical design, the device showed an extremely high efficacy of 114 lm/W at 1000 cd/m². The device also showed 102 lm/W with long lifetime (LT70) of over 10,000 h at 3000 cd/m². Outstanding external quantum efficiency of almost 50% was also achieved in a flat panel with an emissive area of 25 cm². Color coordinates of the panel met the Energy Star ® criteria of solid‐state lighting with CIE (Commission Internationale de l'Éclairage) 1931 (x, y) = (0.477, 0.423), and the color rendering index was 81.     

Ink‐jet‐printable phosphorescent organic light‐emitting‐diode devices

Abstract— A novel method for the fabrication of ink‐jet‐printed organic light‐emitting‐diode devices is discussed. Unlike previously reported solution‐processed OLED devices, the emissive layer of OLED devices reported here does not contain polymeric materials. The emission of the ink‐jet‐printed P²OLED (IJ‐P²OLED) device is demonstrated for the first time. It shows good color and uniform emission although it uses small‐molecule solution. Ink‐jet‐printed green P²OLED devices possess a high luminous efficiency of 22 cd/A at 2000 cd/m² and is based on phosphorescent emission. The latest solution‐processed phosphorescent OLED performance by spin‐coating is disclosed. The red P²OLED exhibits a projected LT50 of >53,000 hours with a luminous efficiency of 9 cd/A at 500 cd/m². The green P²OLED shows a projected LT50 of >52,000 hours with a luminous efficiency of 35 cd/A at 1000 cd/m². Also discussed is a newly developed sky‐blue P²OLED with a projected LT50 of >3000 hour and a luminous efficiency of 18 cd/A at 500 cd/m².     

Development of a phosphorescent white OLED with extremely high power efficiency and long lifetime

Abstract— A white OLED device with extremely high power efficiency and long lifetime was developed, in which blue, yellow‐green, and red phosphorescent emitters were used. The performances achieved were 64 lm/W and 10,000 hours of lifetime at an initial luminance of 1000 cd/m² by using a light outcoupling technique. The device also exhibited the good durability important for practical usage. New technologies, such as blue phosphorescent materials and a sophisticated organic layer structure, were applied to the device. Hopefully, these technologies will open the door to the practical use of OLEDs as light sources.     

Printable phosphorescent organic light‐emitting devices

Abstract— A new approach to full‐color printable phosphorescent organic light‐emitting devices (P²OLEDs) is reported. Unlike conventional solution‐processed OLEDs that contain conjugated polymers in the emissive layer, the P²OLED's emissive layer consists of small‐molecule materials. A red P²OLED that exhibits a luminous efficiency of 11.6 cd/A and a projected lifetime of 100,000 hours from an initial luminance of 500 cd/m², a green P²OLED with a luminous efficiency of 34 cd/A and a projected lifetime of 63,000 hours from an initial luminance of 1000 cd/m², a light‐blue P²OLED with a luminous efficiency of 19 cd/A and a projected lifetime 6000 hours from an initial luminance of 500 cd/m², and a blue P²OLED with a luminous efficiency of 6.2 cd/A and a projected lifetime of 1000 hours from an initial luminance of 500 cd/m² is presented.     

Fluorescent‐based tandem white OLEDs designed for display and solid‐state‐lighting applications

Abstract— Highly efficient tandem white OLEDs based on fluorescent materials were developed for display and solid‐state‐lighting (SSL) applications. In both cases, the white OLED must have high power efficiency and long lifetime, but there are a number of attributes unique to each application that also must be considered. Tandem OLED technology has been demonstrated as an effective approach to increase luminance, extend OLED lifetime, and allow for use of different emitters in the individual stacks for tuning the emission spectrum to achieve desired performance. Here, examples of bottom‐emission tandem white OLEDs based on small‐molecule fluorescent emitters designed for displays and for SSL applications are reported. A two‐stack tandem white OLED designed for display applications achieved 36.5‐cd/A luminance efficiency, 8500K color temperature, and lifetime estimated to exceed 50,000 hours at 1000 cd/m². This performance is expected to meet the specifications for large AMOLED displays. A two‐stack tandem white OLED designed for SSL applications achieved 20‐lm/W power efficiency, 38‐cd/A luminance efficiency, 3500K color temperature, and lifetime estimated to exceed 140,000 hours at 1000 cd/m². With the use of proven light‐extraction techniques, it is estimated that this tandem device will exceed 40 lm/W with more than 500,000‐hour lifetime, performance that should be sufficient for first‐generation lighting products.     

White stacked OLED with 38 lm/W and 100,000‐hour lifetime at 1000 cd/m2 for display and lighting applications

Abstract— The three critical parameters in determining the commercial success of organic light‐emitting diodes (OLEDs), both in display and lighting applications, are power efficiency, lifetime, and price competitiveness. PIN technology is widely considered as the preferred way to maximize power efficiency and lifetime. Here, a high‐efficiency and long‐lifetime white‐light‐emitting diode, which has been realized by stacking a blue‐fluorescent emission unit together with green‐ and red‐phosphorescent emission units, is reported. Proprietary materials have been used in transport layers of each emission unit, which significantly improves the power efficiency and stability. The power efficiency at 1000 cd/m² is 38 lm/W with CIE color coordinates of (0.43, 0.44) and a color‐rendering index (CRI) of 90. An extrapolated lifetime at an initial luminance of 1000 cd/m² is above 100,000 hours, which fulfils the specifications for most applications. The emission color can also be easily tuned towards the equal‐energy white for display applications by selecting emitting materials and varying the transport‐layer cavities.     

Characteristics of a high‐Xe‐concentration 4‐in. PDP

The performance of two 4‐in. color PDP test panels with a default and a high‐Xe‐concentration gas mixture will be discussed. The default panel with a gas mixture of 3.5% Xe in Ne and a filling pressure of 665 hPa was compared with a panel containing a gas mixture of 13.5% Xe in Ne and a filling pressure of 800 hPa. The panels contain a green phosphor, YBO₃:Tb, which showed less saturation at high UV load compared with a Willemite phosphor. The panel performance was compared in addressed conditions. For the default panel, a white luminance of 710 cd/m² and an efficacy of 1.6 lm/W was found, while for the high‐Xe‐partial‐pressure panel, a white luminance of 2010 cd/m² and an efficacy of 3.8 lm/W was realized. The increase of the driving voltages, about 20–30 V, is moderate. Finally, color saturation is improved at high Xe partial pressure.     

Red‐phosphorescent OLEDs employing bis(8‐quinolinolato)phenolato‐aluminum(III) complexes as emission‐layer hosts

Abstract— We have used bis(8‐quinolinolato)phenolato‐aluminum complexes as emission‐layer hosts in red‐phosphorescent OLED devices. This enabled high‐efficiency long‐lived OLED devices with a simple device structure that does not require a hole‐blocking layer. Devices with a red‐phosphorescent dopant introduced into a noble bis(8‐quinolinolato)phenolato‐aluminum complex exhibited a high efficiency of 12 cd/A at CIE color coordinates (0.65, 035) and a long operating lifetime of 30,000 hours or more at an initial luminance of 700 cd/m². Moreover, triplet‐triplet annihilation was reduced in the devices because of the wide emission zone enabled by the complex and the short phosphorescent lifetime of the red‐phosphorescent dopant. We have successfully incorporated these red‐phosphorescent devices into commercial OLED displays.     

A new wettability‐control technique for fabricating color OLED panels by an ink‐jet‐printing method

Abstract— The fabrication technique for color OLED panels by means of wettability‐controllable hole‐injection material (HIM) and a photocatalytic lithography method achieves both precise ink‐jet printing and long‐lifetime devices. The technique enables us to selectively change the non‐wetting surface of a hole‐injection layer (HIL) of metal‐oxide nanoparticles (MONPs) into a wetting surface without damage to the device performance. Wetting patterns formed by this method with photocatalyst‐coated photomasks made it possible to print emission material with patterns of precisely 98‐μm widths on the hole‐injection layer. A fluorescent green‐emitting device fabricated with an HIM of MONPs by the photocatalytic treatment exhibited a long lifetime of 365 hours at30,000 cd/m², which can be extrapolated to a lifetime of more than 110,000 hours at 1000 cd/m², assuming an acceleration coefficient of 1.7. A two‐color device and a monochrome passive‐matrix panel were also successfully fabricated. The two‐color device emitted light without the mixing of colors. The monochrome panel displayed alphabetical characters with good uniformity and no flaws.     

Realization of high efficacy white organic light emitting diode by controlling internal light absorption and angular distribution

We investigated highly efficient organic light emitting diode (OLED) with advanced optical designs of organic layers to convert evanescent mode (internal absorption) into guided light and micro structure to extract the specifically distributed guided light dominated by wide angular substrate mode. White OLED device based on these optical designs realized high efficacy of 133 lm/W and external quantum efficiency of 56 % at 1000 cd/m².     

Composite silver electrode for double‐sided‐emitting stacked organic light‐emitting diode

Abstract— A reflective composite silver electrode is proposed and characterized as the middle electrode of a stacked organic light‐emitting diode (OLED) with double‐sided light emission. The proposed electrode is composed of a thermally evaporated stack of LiF (1 nm)/Al (3 nm)/Ag (70 nm) layers. The LiF/Al and the plasma‐treated Ag of the electrode function well as the respective cathode and anode of the bottom‐ and top‐emitting stacked OLEDs, with both being of the non‐inverted type. Power efficiencies of 10.3 and 12.1 lm/W at 100 cd/m² have been measured for bottom‐ and top‐emitting OLEDs, respectively, using dye doping. The stacked OLED having this bipolar middle electrode can be constructed as a two‐terminal‐only device, allowing for simpler driving schemes in double‐side‐emitting passive‐/active‐matrix OLED displays.     

High‐efficacy drive of spatial positive‐column‐discharge PDP with delayed D pulses

Abstract— A thick‐film ceramic‐sheet PDP provides a long sustain discharge gap of 0.45 mm, enabling the use of positive column discharges. The discharges are established in the middle of the discharge space and are completely free from touching the surface of substrates. This allows for the reduction in diffusion losses of the charged particles. To further improve the efficacy, delayed D pulses are applied to the address electrodes during the sustain period. Although the pulses only draw a little current, they perturb the electric field, reducing the peak discharge current and hence resulting in higher efficacy and luminance. The efficacy and luminance increase by 35% and 38%, respectively, with the delayed D pulses. These pulses are incorporated into the contiguous‐subfield erase‐addressing drive scheme for TV application. A short gap of 70 μm between the sustain and data electrodes generates a fast‐rising discharge and allows a high‐speed addressing of 0.25 μsec. This provides 18 contiguous subfields for the full‐HD single‐scan mode, with 70% light emission duty. A luminous efficacy of 6.0 lm/W can been attained using Ne + 30% Xe 47 kPa, a sustain voltage of 320 V, and a sustain frequency of 3.3 kHz, when the luminance is 157 cd/m². Alternatively, the panel can achieve 4.2 lm/W and 1260 cd/m² by increasing the sustain frequency to 33 kHz.     

PIN OLEDs — Improved structures and materials to enhance device lifetime

Abstract— Currently, three issues are identified that decide upon the commercial success of organic light‐emitting diodes (OLEDs), both in display and lighting applications: power efficiency, lifetime, and price competitiveness. PIN OLEDs are widely seen as the preferred way to maximize power efficiency. Here, it is reported that this concept also delivers the world longest lifetimes. For a highly efficient deep‐red PIN OLED, a half‐lifetime of 25,000 hours for a starting brightness of 10,000 cd/m² and a minimal voltage increase over lifetime is reported. This value corresponds to more than 1 × 10⁶ hours at 1000 cd/m² using an exponent of n = 1.7, which was measured by driving the OLEDs at different starting luminances. Because there is no initial luminance drop, these PIN OLEDs also exhibit a very high 80% lifetime (>300,000 hours at 1000 cd/m²). New record lifetime values for blue and green will be reported as well. Additionally, further topics that have impact on the production yield and cost such as the newly developed air‐stable organic n‐doping material NDN‐26 and top‐emitting structures will be discussed.     

High‐luminance and highly luminous‐efficient AC‐PDP with DelTA cell structure

To improve PDP performance, we developed an AC‐PDP with the Delta Tri‐Color Arrangement (DelTA) cell structure and arc‐shaped electrodes. The experimental panel has a pixel pitch of 1.08 mm and luminous efficacy of 3 lm/W at a luminance of 200 cd/m² despite its conventional gas mixture of Ne and Xe (4%) and conventional phosphor set. Moreover, its peak luminance can be greater than 1000 cd/m². The strong dependence of luminous efficacy on the sustain voltage is also discussed in this paper.     

Optimized LCD backlight for outdoor and high‐brightness applications

A high‐intensity backlight for use with large LCD panels has been developed. It supports the performance and environmental requirements of a display intended for outdoor applications. This backlight technology uses an inductively coupled electrodeless fluorescent lamp with a lifetime of 100,000 hours, instant starting at ?40°C and a stable light output over a temperature span of 70°C. The backlight design has been optimized for luminance uniformity and efficiency within a display depth of 6 in. A 21.3‐in. LCD monitor, using this backlight technology, provides an image brightness of 2000 cd/m² from a single 150‐W lamp.     

Inorganic EL devices with high‐performance blue phosphor and application to 34‐in. flat‐panel televisions

Abstract— A high‐performance inorganic electroluminescence (EL) device has been successfully developed by using an EL structure with a thick dielectric layer (TDEL) and sputtered BaAl₂S₄:Eu blue phosphor. The luminance and efficacy were higher than 2300 cd/m² and 2.5 lm/W at L⁶⁰, 120 Hz, respectively. Furthermore, the luminance at L⁶⁰, 1.2 kHz was more than 23,000 cd/m². The phosphor layer has a single‐phase and a highly oriented crystalline structure. The phosphor also shows high stability in air. A 34‐in. high‐definition television (HDTV) has been developed by combining a TDEL structure and color‐conversion materials. The panels with an optimized color filter demonstrated a peak luminance of 350 cd/m², a color gamut of more than 100% NTSC, and a wide viewing angle similar to that of plasma‐display panels. The high reproducibility of the 34‐in. panels using our pilot line has been confirmed.     

LCD backlights: with or without Hg?

High luminance and efficacy vs. temperature independence and environmental protection: these are the determining factors for the choice of Hg or Xe for LCD backlights. A capacity‐coupled cylindrical Hg discharge lamp attains a luminance of 114,000 cd/m² and an efficacy of 35 lm/W when driven at 5 MHz. On the other hand, a mercury‐free Xe flat discharge backlight produces 11,000 cd/m² and 30 lm/W, with fast luminance response. This paper discusses the underlying limitations assessed to the Hg and Xe backlights, considering application to LC TVs.     

High‐efficiency p‐i‐n organic light‐emitting diodes with long lifetime

Abstract— High‐performance organic light‐emitting diodes (OLEDs) are promoting future applications of solid‐state lighting and flat‐panel displays. We demonstrate here that the performance demands for OLEDs are met by the PIN (p‐doped hole‐transport layer/intrinsically conductive emission layer/n‐doped electron‐transport layer) approach. This approach enables high current efficiency, low driving voltage, as well as long OLED lifetimes. Data on very‐high‐efficiency diodes (power efficiencies exceeding 70 lm/W) incorporating a double‐emission layer, comprised of two bipolar layers doped with tris(phenylpyridine)iridium [Ir(ppy)₃], into the PIN architecture are shown. Lifetimes of more than 220,000 hours at a brightness of 150 cd/m² are reported for a red PIN diode. The PIN approach further allows the integration of highly efficient top‐emitting diodes on a wide range of substrates. This is an important factor, especially for display applications where the compatibility of PIN OLEDs with various kinds of substrates is a key advantage. The PIN concept is very compatible with different backplanes, including passive‐matrix substrates as well as active‐matrix substrates on low‐temperature polysilicon (LTPS) or, in particular, amorphous silicon (a‐Si).     

Very‐high‐brightness diodes for passive‐matrix display applications

Abstract— The development of a high‐brightness low‐voltage yellow‐light‐emitting polymer system suitable for use in low‐cost passive‐matrix displays will be reported. Average device efficiencies of 16 lm/W at 100 and 1000 cd/m² are achieved at 2.1 and 2.4 V, respectively. A luminance level of 100,000 cd/m² is achieved at 5.5 V.