PIN‐OLEDs for active‐matrix‐display use

Abstract— Novaled's PIN‐OLED® technology allows for highly efficient, temperature stable, and long‐lived OLEDs suited for a variety of display applications. This paper delivers an overview about Novaled's state of the art, including top‐ and bottom‐emitting structures. It is discussed how PIN‐OLEDs give rise to an increased manufacturing yield. The main focus of this paper is the development of white OLEDs for display use. When the RGBW color‐filter approach is used in combination with white OLEDs, the resulting full‐color OLED display is able to deliver high color quality and remain highly power efficient. For such a case, the manufacturing infrastructure of OLEDs for lighting can be used. We use tandem architectures, bottom‐ and top‐emission architectures, and developed specific high‐temperature stable OLED stacks. The importance of matching color coordinates of the white OLED and the targeted display white color point is of outstanding importance. Results have mainly been achieved under the German‐funded project CARO and the European‐funded project AMAZOLED.     

Full‐color AMOLED with RGBW pixel pattern

Abstract— A full‐color AMOLED display with an RGBW color filter pattern has been fabricated. Displays with this format require about one‐half the power of analogous RGB displays. RGBW and RGB 2.16‐in.‐diagonal displays with average power consumptions of 180 and 340 mW, respectively, were characterized for a set of standard digital still camera images at a luminance of 100 cd/m². In both cases, a white‐emitting AMOLED was used as the light source, and standard LCD filters were used to provide the R, G, and B emission. The color gamuts of these displays were identical and the higher overall efficiency of the RGBW format results from two factors. First, a large fraction of a typical image is near neutral in color and can be reproduced using the white sub‐pixel. Second, the white sub‐pixel in an RGBW AMOLED display is highly efficient because of the absence of any color filter. The efficiency of these displays can be further enhanced by choosing a white emitter optimized to the target display white point (in this case D65). A two‐emission layer configuration based upon separate yellow and blue‐emitting regions is shown to be well suited for both the RGBW and RGB formats.     

White‐emitting OLED devices in an RGBW format with microelement white subpixels

Abstract— OLED devices with an RGBW pixel format using an unpatterned white emitter have the potential to provide very good efficiency and color gamut while enabling lower‐cost and large‐format manufacturing. However, the white subpixel often has unacceptably large color shifts with viewing angle. Furthermore, for some architectures such as top‐emitting microcavity devices, it can even be difficult to produce a white subpixel with good on‐axis color. In this paper, we describe the use of a white subpixel made up of a combination of differently tuned microelements and demonstrate how such an approach can overcome these problems. By carefully tuning the color and areas of each of the microelements in the white subpixel, we can trade off between better on‐axis color, less color change with angle, and higher efficiency. Furthermore, it was demonstrated that an RGBW top‐emitter microcavity device with a microelement white subpixel can achieve an increase in both power efficiency and color gamut relative to a conventional RGBW bottom‐emitter non‐microcavity device.     

Micro‐cavity design of bottom‐emitting AMOLED with white OLED and RGBW color filters for 100% color gamut

Abstract— Two optical structures used for a bottom‐emitting white organic light‐emitting diode (OLED) is reported. An RGBW color system was employed because of its high efficiency. For red, green, and blue (RGB) subpixels, the cavity resonance was enhanced by the use of a dielectric mirror, and for the white (W) subpixel, the mirror was removed. The optical length of the cavities was controlled by two different ways: by the thickness of the dielectric filter on top of the mirror or by the angle of oblique emission. With both methods, active‐matrix OLEDs (AMOLEDs) that reproduced a color gamut exceeding 100% of the NTSC (National Television System Committee) standard were fabricated. More importantly, the transmission of a white OLED through R/G/B color filters was significantly higher (up to 50%) than that of a conventional structure not employing a mirror, while at the same time as the color gamut increased from ～75 to ～100% NTSC.     

RGB‐to‐RGBW conversion with current limiting for OLED displays

Abstract— Organic‐light‐emitting‐diode (OLED) displays employing white‐light‐emitting OLEDs in combination with RGBW color filters can demand high peak currents to present images with bright, highly saturated colors. Image‐processing methods that take advantage of a very highly efficient white subpixel in addition to filtered RGB subpixels to reduce the peak current and power of these displays are described. The image‐quality impact of these algorithms are explored to develop a final image‐processing algorithm.     

15‐in. RGBW panel using two‐stacked white OLED and color filters for large‐sized display applications

Abstract— A 15‐in. HD panel employing two‐stacked WOLEDs and color filters for which the color gamut can be as high as 101.2% (CIE1976) and the power consumption is 5.22 W. The WOLEDs exhibit a current efficiency of 61.3 cd/A and a power efficiency of 30 lm/W at 1000 nits and their CIE coordinate is (0.340, 0.334). A 15‐in. RGBW panel was investigated to verify the electrical and optical performance compared to that of a 15‐in. RGB TV made by using FMM technology. The characteristics of the 15‐in. RGBW panel are comparable to those of the 15‐in. RGB panel. Color filters combined with WOLEDs is a possible patterning technology for large‐sized OLED TV, which surpasses the limits of fine‐metal‐mask technology.     

Microcavity white‐emitting OLED devices

Abstract— Microcavity designs for OLED devices with an unpatterned white emitter have the potential to provide greater brightness and larger color gamut than non‐microcavity designs while still enabling lower‐cost large‐format manufacturing. In this paper, such microcavity and non‐microcavity designs are compared. Color filters must still be employed to provide an adequate color gamut. Top‐emitter structures have somewhat greater on‐axis luminance and color gamut, but increased angular change, than bottom‐emitter designs. In a single‐stack bottom‐emitter active‐matrix TFT device using an RGBW format, the use of microcavities is estimated to reduce the average power usage by 35% and the peak power by 58%, while increasing the NTSC ratio for color gamut area by about 10%. Angular luminance and color change is likely to be acceptable, especially for hand‐held applications. Tandem devices employing multiple emitter stacks increase the lifetime of OLED devices but require larger driving voltages; for such devices, microcavity structures are useful although the percentage reduction obtained in power usage is not quite as large. Generally, tandem devices with microcavities have a slightly stronger cavity effect yielding slightly larger color gamut, but also greater angular color and luminance shift. Therefore, microcavity architectures are less appealing for tandem devices.     

Compact and efficient RGB to RGBW data conversion method and its application in OLED microdisplays

In many electronic information displays, a colour pixel comprises three spatially distinct sub‐pixels containing red, green and blue (RGB) colour filters. The option of adding a fourth white (W) sub‐pixel that allows light to pass through unfiltered can significantly improve the optical efficiency of the pixel that, in turn, increases the power efficiency of the display. Such a display is called an RGBW display, and the required transformation of data format from incoming RGB to pixel RGBW is termed as “RGB to RGBW conversion.” This paper reports a method of RGB to RGBW conversion that is highly compact and efficient in terms of system resources while retaining image quality. It processes incoming data through a new colour space conversion algorithm in order to reduce the average power consumption with no noticeable visual artefacts. We explain the method and demonstrate its cost‐effective and power‐effective implementation for the specific case of an organic light emitting diode microdisplay.     

Fabrication of flexible organic light‐emitting‐diode display with a flexible color filter driven by In—Ga—Zn—Oxide TFTs

Abstract— A novel flexible active‐matrix organic light‐emitting‐diode (OLED) display fabricated on planarized stainless—used‐steel substrates with a resolution of 85 dpi in a 4.7‐in. active area has been demonstrated. Amorphous indium—gallium—zinc—oxide thin‐film transistors were used as the backplane for the OLED display with high device performance, high electrical stability, and long lifetime. A full‐color moving image at a frame frequency of 60 Hz was also realized by using a flexible color filter directly patterned on a plastic substrate with a white OLED as the light source.     

Flexible high‐resolution full‐color top‐emitting active‐matrix organic light‐emitting diode display

We developed a high‐performance 3.4‐in. flexible active‐matrix organic light‐emitting diode (AMOLED) display with remarkably high resolution using an oxide semiconductor in a backplane, by applying our transfer technology that utilizes metal separation layers. Using this panel, we also fabricated a prototype of a side‐roll display for mobile uses. In these AMOLED displays, a white OLED combined with a color filter was used in order to achieve remarkably high resolution. For the white OLED, a tandem structure in which a phosphorescent emission unit and a fluorescent emission unit are serially connected with an intermediate layer sandwiched between the emission units was employed. Furthermore, revolutionary technologies that enable a reduction in power consumption in both the phosphorescent and fluorescent emission units were introduced to the white tandem OLED.     

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.     

A 3.0‐in. 308‐ppi WVGA AMOLED with a top‐emission white OLED and color filter

Abstract— A 3.0‐in. 308‐ppi WVGA top‐emission AMOLED display with a white OLED and color filters, driven by LTPS TFTs demonstrating a color gamut of >90% and a Δ(u′,v′) of <0.02 is reported. A white‐emission source with a unique device structure was developed using all fluorescent materials and yielded efficiencies of 8.45% and 16 cd/A at 4000 nits with CIE color coordinates of (0.30, 0.32).     

A dual‐gap RGBW transflective TFT‐LCD with adjustable color gamut

Abstract— An adjustable‐color‐gamut dual‐gap RGBW transflective liquid‐crystal display that uses a four‐color manufacturing process and a color‐processing algorithm to achieve the appropriate color performance in both the transmissive and reflective modes is presented. Based on superior‐color‐transformation units, the total brightness and color gamut can be modified under different ambience. The highest NTSC color gamut in the reflective mode (reflectance, 4.4%) that has been fabricated successfully for a RGBW 1.5‐in. dual‐gap panel is 23% with a 7%, 17%, and 40% NTSC color gamut in the transmissive mode by using different algorithms. Compared to a typical RGB panel, it not only provides flexibility for any environment but also satisfies a variety of personal requirements. Based on personal preference, users have more choices to adjust the LCD settings such as color saturation, brightness, etc. The smart RGBW TRLCD will definitely become the developing trend towards sunlight‐readable LCDs in the near future.     

An 18 megapixel 4.3″ 1443 ppi 120 Hz OLED display for wide field of view high acuity head mounted displays

We developed and fabricated the world's highest resolution (18 megapixel, 1443 ppi) OLED on glass display panel. The design uses a white OLED with color filter structure for high density pixelization and an n‐type LTPS backplane for faster response time than mobile phone displays. A custom high bandwidth driver IC was fabricated. We developed a foveated pixel pipeline appropriate for virtual reality and augmented reality applications, especially mobile systems.     

Neuro-controller for broadcast lighting light-emitting diode to express white light with high color rendering index

Technical characteristics analysis related to correlated color temperature (CCT), color rendering, and illuminance is required to use light-emitting diode (LED) as broadcast lighting. In general, to realize a white light source with a high color rendering index (CRI), we selected the appropriate emission intensity of RGBW LED through trial and error. However, the characteristics of the LED light source and environmental conditions make it difficult to perform the procedure several times. The objective of this study was to design a system that could control illuminance, CCT, and ∆uv while having high CRI, as an LED control method for broadcasting lighting. The controller implements using a feed-forward neural network with excellent nonlinear function approximation capability. We measure data directly from the red green blue white (RGBW) LED system for neural network training. We then select data with high CRI from the measured raw data and choose data for neural network learning by removing measurement noise using the quadratic polynomial interpolation method. The performance evaluation confirms that the proposed neural network controller shows excellent results as an RGBW LED controller for broadcast lighting in the Planckian locus and all regions of white light.     

A 13.5‐in. Quad‐FHD flexible CAAC‐OS AMOLED display with long‐life OLED device structure

In this study, the device structure of a white tandem organic light‐emitting diode (OLED) was changed to control the emission area and thereby achieve less luminance decay. A long‐life 13.5‐inch 4 K flexible c‐axis‐aligned crystal oxide semiconductor (CAAC‐OS) active‐matrix OLED with less color shift and high resolution was fabricated using this long‐life white OLED, transfer technology, and a CAAC‐OS field‐effect transistor.     

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.     

A first demonstration and analysis of the biprimary color system for reflective displays

A new biprimary color system is demonstrated for single‐layer reflective displays, capturing much of the improved color performance of multilayer displays while potentially maintaining single‐layer display advantages in high resolution and faster switching. Electrophoretic pixels were operated with dual‐particle complementary‐colored dispersions such as green/magenta (G/M). Using simple interdigitated three‐electrode architecture, four colored states (KWGM) were achieved with a preliminary contrast ratio of 10 : 1. Furthermore, biprimary ink dispersions were shown to be functional in a more advanced electrokinetic pixel structure. A full‐color biprimary pixel contains three complementary subpixels (G/M, B/Y, R/C), and the requisite electrophoretic ink dispersions were also formulated and spectrally characterized in this work. Lastly, theoretical color space mapping confirms that the biprimary concept provides twice the brightness and twice the color fraction compared with the conventional RGBW subpixel approach, and that the biprimary concept can approach performance close to that of magazine print (Specifications for Web‐Offset Print).     

Flexible active‐matrix OLED displays: Challenges and progress

Abstract— Organic light‐emitting‐device (OLED) devices are very promising candidates for flexible‐display applications because of their organic thin‐film configuration and excellent optical and video performance. Recent progress of flexible‐OLED technologies for high‐performance full‐color active‐matrix OLED (AMOLED) displays will be presented and future challenges will be discussed. Specific focus is placed on technology components, including high‐efficiency phosphorescent OLED technology, substrates and backplanes for flexible displays, transparent compound cathode technology, conformal packaging, and the flexibility testing of these devices. Finally, the latest prototype in collaboration with LG. Phillips LCD, a flexible 4‐in. QVGA full‐color AMOLED built on amorphous‐silicon backplane, will be described.     

World's first large size 77‐inch transparent flexible OLED display

Large flexible organic light‐emitting diode (OLED) display provides various electronic applications such as curved, bendable, rollable, and commercial display, because of its thinness, light weight, and design freedom. In this work, the process flow and key technologies to fabricate the world's first large size 77‐inch transparent flexible OLED display are introduced. “White OLED on TFT + color filter” method is used to fabricate the aforementioned display. On both thin‐film transistor and color filter substrates, transparent polyimide (PI) was used as plastic substrate with multi‐barrier. In case of a transparent flexible display, the multi‐barrier is required for the additional consideration to overcome the decrease of transmittance due to the difference in refractive index of the conventional multi‐barrier. We developed the special multi‐barrier to increase transparency with superior water vapor transition rate characteristic. The optimized amorphous indium gallium zinc oxide thin‐film transistors were employed on the multi‐barrier, and it shows the highly uniform electrical performance and reliability on plastic substrate. Also, the typical panel failure mechanism during laser lift‐off process caused by a particle in PI is studied, and a sacrificial layer was suggested between PI and a carrier glass to reduce the panel failure. Finally, we successfully realized the world's first 77‐inch transparent flexible OLED display with ultra‐high‐definition resolution, which can be rolled up to a radius of 80 mm with a transmittance of 40%.