Surface‐light‐emitting transistors based on vertical‐type metal‐base organic transistors

Abstract— Light‐emitting transistors having a metal‐base organic transistor (MBOT) structure demonstrate both the function of an organic thin‐film transistor (OTFT) and organic light‐emitting diode (OLED). The MBOT is a vertical‐type organic transistor having a simple structure composed of organic/metal/organic layers demonstrating high‐current and low‐voltage operation. The light‐emitting MBOT was fabricated simply by inserting additional layers of hole‐transporting and emissive materials used in the OLED into the col lector layer. The device showed perfect surface emission similar to an OLED. A luminance modulation of 370 cd/m² was observed at a collector voltage of 20 V and a base voltage of 3 V. This device can be applied to an OLED display device to increase the numerical aperture or reduce the required current of the TFT backplane.     

Microdisplay‐based industrial 3‐D and microstructure measurement systems

Abstract— Microdisplays, whether they are of the liquid‐crystal‐on‐silicon (LCOS) or organic light‐emitting diode (OLED) type, have been, up until now, mainly used in multimedia applications or head‐mounted displays. Due to their interesting possibilities, these displays open more and more alternative applications; for example, in optical metrology. Projection lenses for this application area need to be specially designed because the requirements on these systems differ completely from those for multimedia applications. The lenses must have very low geometrical image distortion and they have to be adapted to small objects and/or image distances. On the other hand, they often work with light sources with small spectral bandwidths; consequently, they do not need to be corrected for chromatic aberrations. In addition, the numerical aperture has to be large enough to collect and transfer as much light as possible, but also the size of the projection lens has to be as small as possible to ensure compact measurement systems. All these requirements lead to a compromise in optical lens design. Three optical system designs and realizations — one with an OLED microdisplay and two with an LCOS microdisplay — are presented.     

Recent development of soluble hole injection material for OLED display

We developed soluble hole injection materials and inks, named ELsource, that can be used as hole injection layer in organic light‐emitting diode (OLED) display. OLED is an optical device. Therefore, we developed the hole injection materials with optical properties necessary for an optical device.     

Organic polymer thick film light emitting diodes (PTF-OLED)

A guest–host approach was used to fabricate a one-layer organic light emitting diode (OLED). The thick film ink approach allows the two-dimensional OLED to be processed using traditional methods such as silk-screen printing. The I–V–L characteristics of the polymer thick film (PTF)-OLED were studied as a function of the device chemical compositions and physical configurations. Different polymers, hole and electron transporters, and emitters at different weight ratios were studied for its composition dependence. Device configuration also plays a significant role on its overall performance. Dependence on film thickness, electrode type, and the usage of additional charge injection layers were also investigated. The simplified one-layer device allows a straightforward interpretation for the charge-transport and recombination phenomena which shed light for its future improvement.     

Phosphorescent OLEDs: Enabling energy‐efficient lighting with improved uniformity and longer lifetime

Abstract— In this paper, the design criteria for scaling up from small‐area organic light‐emitting‐diode (OLED) pixels to large‐area OLED light panels is described. Particular focus is placed on using phosphorescent OLEDs (PHOLEDs) to maximize panel efficacy and uniformity and minimize operating temperature. Data for a pair of all‐phosphorescent 15 × 15 cm OLED light panels are also presented: Panel 1 has 62‐lm/W efficacy, CRI = 81, CCT = 3180K, and lifetime to LT70 = 18,000 hours at 1000 cd/m² and Panel 2 has 58‐lm/W efficacy, CRI = 82, CCT = 2640K, and lifetime to LT70 = 30,000 hours at 1000 cd/m². Operating at a 3000 cd/m² (7740 lm/m²), Panel 2 has 49‐lm/W efficacy with lifetime to LT70 = 4000 hours. Excellent panel lifetime is enabled by a stable light‐blue phosphorescent materials system and by the use of efficient phosphorescent emitters that ensure very low panel temperature without any additional thermal management.     

Development of a color‐tunable polychromatic organic‐light‐emitting‐diode device for roll‐to‐roll manufacturing

A flexible vertically stacked flexible polychromatic color‐tunable OLED has been developed by means of low resistive intermediate electrode technology. The polychromatic OLED has a capability to show 16 million colors with 105% National Television Committee Standard (NTSC) color reproduction. The device can produce arbitrary shape with arbitrary colors, suitable for artistic expressions, just as many as those used in information displays. Independently controlled red, green, and blue light‐emitting layers are stacked vertically. With conventional indium tin oxide technology, because of the temperature restriction, it was quite difficult to achieve low resistance on plastic substrate. The reported numbers were all more than 80 Ω/□. According to the surface mobility control using Fick's law analysis, low sheet resistance 7.34 Ω/□ on plastic film was developed. At first, flexible 7.17 cm² transparent OLED was fabricated for the performance confirmation of transparent electrode. And then polychromatic color‐tunable OLED with the same size were successfully fabricated on plastic. With optical length optimization for each color stack of polychromatic OLED, more than 100% color reproduction in National Television Committee Standard was achieved by stack design. The polychromatic device can be used for colored illumination, as well as for organic‐light‐emitting display pixels for three times emission than conventional pixel design. The device is fabricated on plastic substrate so that the polychromatic organic‐light‐emitting‐diode device is manufacturable with roll‐to‐roll production line.     

High‐efficiency OLED microdisplay with microlens array

A high‐efficiency organic light‐emitting diode (OLED) microdisplay has been developed with some new technologies including microlens array. We focused on the improvement of the out‐coupling efficiency and achieved three times higher efficiency as compared with conventional OLED. By using our developed technologies, it is possible to improve the maximum luminance from 1600 to 5000 cd/m² while maintaining same lifetime.     

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.     

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.     

Repeatedly foldable AMOLED display

In this study, a 5.9‐inch foldable active‐matrix organic light emitting diode (AMOLED) display was developed. A folding test was performed repeatedly. The display survived the folding test (100,000 folds) with a curvature radius of 2 mm. To protect an organic light emitting diode (OLED) against moisture, inorganic passivation layers are provided on the upper and lower sides of the flexible display. Using our transfer technology, high density passivation layers can be obtained. The measured water vapor transmission rate of the layer is 7 × 10^?6 g/m²?day or less, which improves OLED reliability. With these techniques, we have developed a book‐type display, which is repeatedly foldable like a book, and a tri‐fold display including a display area, which is foldable in three.     

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.     

Realization of RGB colors from top‐emitting white OLED by electron beam patterning

We demonstrate the realization of red, green, and blue colors from top‐emitting white organic light‐emitting diode (OLED) for display applications. In our approach, red, green, and blue colors are realized by microcavity‐based mode selection from the spectrum of a white OLED. For the tuning of individual microcavities, the OLED hole transport layer is patterned by an electron beam process.     

Novel front‐light system using fine‐pitch patterned OLED

Abstract— A novel front‐light system that uses an organic light‐emitting‐diode (OLED) light source patterned with a fine pitch has been developed. The front‐light system has the following characteristics: (1) excellent uniformity within the light‐emitting area; (2) emittance that is consistent at all viewing angles; (3) no light leakage at any viewing angle from the side of the observer. This system can be adopted for reflective LCDs, electrophoretic displays (EPDs), microelectromechanical systems (MEMS), and other applications.     

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.     

Development of flexible organic light‐emitting diode on barrier film and roll‐to‐roll manufacturing

To come out with a successful organic light‐emitting diode (OLED) lighting business, it is very important to have clear differentiation of OLED from LEDs. Flexible OLED has merits, such as capability to be mounted on the curved wall, which is not easy for LEDs to achieve the feature. There are several approaches to make flexible OLEDs especially among those plastic barrier films that can bring high level of flexibility, which could not be achieved by any conventional lighting method. In this paper, barrier films with various water vapor transmission rate values, including 10^{? 6} order, are applied, and the conditions to have almost no dark spot growth under 85 °C and 85% high temperature/humidity test are shown. Flexible OLED panels are manufactured with the world's first roll‐to‐roll equipment using plastic barrier film.     

The liquid crystal light valve,an optical-to-optical interface device

A new device is described that transfers high resolution, two-state (black and white) images from a noncoherent beam of light to a fully coherent beam of light in quasi real-time (less than 1 sec). The device is a photoconductor activated liquid crystal light valve that operates in the dynamic scattering mode of the liquid crystal. It has sensitivity of 1–10 μW/cm² (at 5100 Å), resolution of 100 lines/mm and cycles on and off in 0.25 sec or less. This paper describes the construction and operation of the device and discusses its application to coherent optical data processing.     

OLED‐based pico‐projection system

Abstract— Two pico‐projection systems, a monochrome green and a full‐color system, based on high‐efficiency OLED microdisplays (VGA; pixel size, 12 μm) are presented. Both optical systems are described by a numerical aperture of about 0.3, a magnification of 15x, and a working distance of 300–360 mm. The frequency limit of both systems is 42 cycles/mm at an image contrast of about 60%. The monochrome projection system with a volume smaller than 10 cm³ consists of one green OLED and a projection lens with five elements. The measured luminance in the image plane is about 0.061 lm. The image has a diagonal of 150 mm with a working distance of about 300 mm and has a considerable image contrast of 396:1. The second system combines three high‐brightness OLEDs, red, green, and blue colored, together with a projection lens and an image‐combining element, and an X‐Cube to achieve full‐color projection. The estimated luminance value for the three‐panel projection unit with an OLED luminance of 10,000 cd/m² for each display will be about Φcalculated = 0.147 lm. In this paper, the system concepts, the optical designs, and the realized prototypes of the monochrome and full‐color projection system are presented.     

Vertically integrated,double stack oxide TFT layers for high‐resolution AMOLED backplane

We developed a novel vertically integrated, double stack oxide thin‐film transistor (TFT) backplane for high‐resolution organic light‐emitting diode (OLED) displays. The first TFT layer is bulk‐accumulation mode, and the second TFT layer is a single gate with back‐channel etched structure. The extracted mobilities and threshold voltages are higher than 10 cm²/Vs and 0 ~ 1 V, respectively. Both TFTs are found to be extremely stable under the bias and temperature stress. The gate driver with width of 530 μm and a pitch of 18.6 μm was developed, exhibiting well shifted signal up to the last stage of 900 stages without output degradation, which could be used for 1360 ppi TFT backplane.     

The effect of transmittance and luminous efficiency with the application of cathode mesh mask in transparent organic light‐emitting devices

With the development of organic light‐emitting devices (OLEDs), the transparent OLED is also restricted by its efficiency and stability. Thus, in order to improve the transmittance and luminous efficiency of transparent OLED, the cathode mesh mask combined with Al:Ag alloy is adopted to prepare the cathode of transparent OLED, which would enhanced the luminance, efficiency, and transmittance of the device. With the same driving voltage, the device has the highest brightness, when the cathode thickness is 85 nm. At the voltage of 13 and 14 V, the luminance, for bottom‐emission and top‐emission, is 9501 cd/m² and 1840 cd/m², respectively. The entire transmittance of the device has achieved about 78% at a 480 nm wavelength.     

Characterization and compensation of OLED aging in a digital AMOLED system

Organic light‐emitting diode (OLED) aging is the root cause for image sticking artifact and considered as the toughest problem besides the low yield problem of active‐matrix organic light‐emitting diode (AMOLED) displays. Digital driving can eliminate Mura artifact and allow a similar yield like LCD. However, it is more prone to OLED aging than analog driving, so that the lifetime will become shorter. In this paper, we pursue the approach to measure the pixel current and compensate OLED I–V drift. Information gained from electrical measurements during the lifetime of the display may be correlated to electro‐optical drift, particularly the current efficiency. The aging model has to consider the dependence of I–V drift and efficiency loss on the operation point/voltage for each subframe. Specific compensation algorithms have been developed. Two AMOLED prototypes (1.5 and 2.8 in.) were validated. Burned‐in pattern can be compensated, so the concept has been proven as effective. With the method described in this paper, digital AMOLED may reach a similar and even significantly higher lifetime than an analog AMOLED.