Top Emission Structure Research Articles

Study on Printable Inorganic Alternating Current Electroluminescence Devices based on Different Electrode Structures

Traditional bottom light emitting devices are commonly limited by the light transmittance of the substrate and electrode, while the recent emerging inorganic alternating current electroluminescence (ACEL) devices, which manifest excellent application prospects in the field of flexible display are mainly prepared by directly mixing thermosetting resin and powder materials. Here, the electrode layer, dielectric layer and light-emitting layer based on different electrode structures, were printed in different orders and structures by the inking technology. Printable inorganic ACEL devices with bottom-emission structure (BES), top-emission structure (TES) and planar electrode structure (PES) were successfully obtained. The measurements of luminescent properties of printable ACEL with different electrode structures under different voltages by spectrometer indicated that BES-ACEL had the best brightness. Besides, TES-ACEL and PES-ACEL have the outstanding advantages of no substrate limitation and interaction characteristics, respectively. Therefore, this work opens up the new path for ACEL devices towards application in the fields of printing and packaging, interactive and intelligent display.

58‐2: Distinguished Paper: Active Matrix QD‐LED with Top Emission Structure by UV Lithography for RGB Patterning

We have developed full colour top emitting quantum dot light emitting diode (QD‐LED) display driven by a 176 ppi active matrix of metal oxide thin film transistors. Red, green and blue (RGB) QD‐LED sub pixel emission layers are patterned by our original UV photolithography process and materials. We also demonstrate the potential to achieve high resolution such as 528 ppi using this process.

Active matrix QD‐LED with top emission structure by UV lithography for RGB patterning

AbstractWe have developed full colour top emitting quantum dot light‐emitting diode (QD‐LED) display driven by a 176‐ppi active matrix of metal oxide thin‐film transistors. Red, green and blue (RGB) QD‐LED subpixel emission layers are patterned by our original UV photolithography process and materials. We also demonstrate the potential to achieve high resolution such as 528 ppi using this process.

Highly Efficient and Bright Inverted Top-Emitting InP Quantum Dot Light-Emitting Diodes Introducing a Hole-Suppressing Interlayer.

InP quantum dots (QDs) based light-emitting diodes (QLEDs) are considered as one of the most promising candidates as a substitute for the environmentally toxic Cd-based QLEDs for future displays. However, the device architecture of InP QLEDs is almost the same as the Cd-based QLEDs even though the properties of Cd-based and InP-based QDs are quite different in their energy levels and shapes. Thus, it is highly required to develop a proper device structure for InP-based QLEDs to improve the efficiency and stability. In this work, efficient, bright, and stable InP/ZnSeS QLEDs based on an inverted top emission QLED (ITQLED) structure by newly introducing a "hole-suppressing interlayer" are demonstrated. The green-emitting ITQLEDs with the hole-suppressing interlayer exhibit a maximum current efficiency of 15.1-21.6 cd A-1 and the maximum luminance of 17 400-38 800 cd m-2 , which outperform the recently reported InP-based QLEDs. The operational lifetime is also increased when the hole-suppressing interlayer is adopted. These superb QLED performances originate not only from the enhanced light-outcoupling by the top emission structure but also from the improved electron-hole balance by introducing a hole-suppressing interlayer which can control the hole injection into QDs.

High-Resolution Flexible AMOLED Display Integrating Gate Driver by Metal–Oxide TFTs

This letter proposes a high-resolution [200 (RGB) * 600, 282 PPI) flexible active matrix organic light emitting display (AMOLED) integrating a new gate driver, of which the substrate is a polyimide material. Flexible In–Zn–O thin-film transistors (TFTs) with back channel etched structure reveal a good stability at different curvature radii. The integrated gate driver employing bi-side driving method consists of seven TFTs and two capacitors with the advantages of simple topology, low power, full-swing output, and small area. The conventional 2T1C pixel circuit with top emission structure is applied to the proposed flexible AMOLED panel. And the flexible panel has a good full-color display quality without obvious defects at the bending condition. It is shown that the output signals of the proposed gate driver have no distortion and good noise suppressed characteristics even up to 600 stages and maintain stable under a long-time continuous operation up to 15 days.

Transparent electrode for top emission organiclight-emitting diode

Organic light-emitting diode (OLED) has been successfully used in mobile display (small area) and television display (large area). For small area display screens, the top emission structure is mostly adopted because of the limitation of display area. Top emission OLED (TEOLED) can get higher power efficiency at the same current density than traditional bottom emission devices because of its higher aperture-opening ratio. However, the most important part of top emission device is the preparation of transparent electrode. In summary, according to the method and material, TEOLED transparent electrode is divided into the following categories: (1) Transparent conductive oxide electrode (TCO); (2) ultrathin composite metal electrode; (3) dielectric/metal/dielectric (DMD) composite electrode; (4) nanomaterial electrodes, etc. The general oxide has great optical transmittance in the visible light range, but the thermal evaporation temperature is very high. It needs to be fabricated by sputtering, which damages the organic layer. The composite metal electrode can be made by thermal evaporation, which is simple and easy. It is adopted by most commercial products by now, however its transparency is relatively low. Nano materials have high transparency and can be fabricated for flexible electrodes, but because of the solution processing, it is easier to destroy the organic layer. DMD composite electrode not only has high transmittance, but also can use thermal evaporation method to form film, it is expected to become better choice of top electrode for TEOLED. In order to achieve the objective of producing top emitting OLED with excellent properties, it is most important to find enough transparent, high conductive, ohmic contact, film forming process without destroying organic layer and stable electrode material. Up to now, the researchers have proposed several methods for preparing barrier layer-ITO, pulsed laser deposition transparent conducting oxide, thermal evaporated ultrathin composite metal, DMD composite, nano-materials, etc. In this paper, the applications of these materials in the TEOLED transparent electrode are reviewed. By comparing the advantages and disadvantages of thin film electrode, the research progress of TEOLED transparent electrode is reviewed.

10‐4: A 13.3‐inch 8K x 4K 664‐ppi 120‐Hz 12‐bit Display with Super‐wide Color Gamut for the BT.2020 Standard

Newly developed light‐emitting materials and device structure achieved a highly efficient long‐lived white tandem OLED with saturated RGB spectra for a wider color gamut. By combining the OLED devices with a color filter and top emission structure, we successfully fabricated a full‐specification 8K AMOLED panel with the BT.2020 color gamut.

Highly Flexible and Bright Electroluminescent Devices Based on Ag Nanowire Electrodes and Top‐Emission Structure

Highly flexible and bright alternating current electroluminescent devices are designed and fabricated with a top emission structure and Ag nanowires serving as both top and bottom electrodes. The devices exhibit simultaneously high luminance (957 cd m−2 @ 195 V and 2 kHz), and unprecedented flexibility as well as mechanical stability, being able to endure a strain as large as 6.5% and to maintain 88.4% luminance after 1000 bending-recovery cycles. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Power Consumption Model for AMOLED Display Panel Based on 2T-1C Pixel Circuit

The display device has a significant contribution to the total power, which is critical for mobile consumer-electronic devices due to a limited battery capacity. We develop a power model of the active-matrix organic light-emitting diode (AMOLED) display and analyze the power contribution of thin-film transistor (TFT), OLED, and ${V_{\rm DD}}$ line drop. Both theoretical analysis and calculation are derived from TFT mobility, OLED luminous efficiency, pixel aperture ratio, and ${V_{\rm DD}}$ line drop. The TFT mobility from ${0.1}$ to ${10}\; \text{cm}^{2}/(\text{V}\cdot \text{s})$ is a bottleneck of display power. Metal oxide TFT may be more suitable for AMOLED display since relatively high mobility and low fabrication temperature. High luminous efficiency of OLED and top emission structure can decrease power consumption abundantly. The impact of copper wire technology is also discussed in large-size panels.

High Efficiency Top-Emission Organic Light Emitting Diodes with Second and Third-Order Microcavity Structure

Top-emitting micro-cavity organic light emitting diodes (TEOLEDs) are now acquiring the center stage as an important candidate for the active matrix display applications. OLEDs with top-emission structure, thicknesses of organic layers over 2000 Å are crucial for the real mass production of OLED. In this paper, we report top-emitting organic light emitting diodes with various strong microcavity structures such as second order, third order microcavity mode, and tandem architecture. We design the device layer structure, especially the location of emissive layer, by simulating the radiance distribution of red, green, and blue emitter as a function of thickness of transporting layers. Furthermore, the quantum efficiency of designed device is estimated. In summary, both optically and electrically simulated results of TEOLEDs are quite well matched with those of actually fabricated devices.

High performance of the organic–inorganic powder electroluminescence device with high color-rendering capability using the multilayer

An AC-driven organic–inorganic hybrid powder electroluminescence (EL) device was made to investigate the effect of organic dye on EL performance. The bluish green emitting-ZnS:Cu,Cl phosphor and coumarin 6 (and DCJTB) were used as emitting material and organic dyes (color converting material), respectively. In order to convert an emission spectrum effectively, an EL device composed of the Al/dielectric layer/composite emitting layer (phosphor–coumarin 6)/red-color-filter layer (DCJTB)/indium tin oxide electrode was prepared using the top-emission structure. At 150V and 10kHz, the organic–inorganic hybrid EL device had a luminance of 780cd/m2 and a color coordinate of (0.65, 0.33) in Commission International de I’Eclairage. The blue emission which originated from ZnS:Cu,Cl at 10kHz was converted into the green emission by coumarin 6. Then, this green emission was converted into red by DCJTB. The high EL intensity and high color-rendering capability were attributed to the color conversion.

9.1: WITHDRAWN: 9.2: New Threshold Voltage Compensation Pixel Circuits in 13.5‐inch Quad Full High Definition OLED Display of Crystalline In‐Ga‐Zn‐Oxide FETs

AbstractWe devised a 5Tr+1C threshold voltage compensation pixel circuit that operates even with a normally‐on transistor. Variations in threshold voltage can be reduced to 25 to 30%. We fabricated a 13.5‐inch quad full high definition (QFHD) OLED display, which has a top‐emission structure using white tandem OLEDs with color filters.

Enhanced Optical and Electrical Properties of Inorganic Electroluminescent Devices Using the Top-Emission Structure

Alternating current inorganic powder electroluminescence (EL) devices with a top-emission structure were fabricated on glass substrates to investigate the structural dependence on EL. The EL performance was examined by comparing the top-emission structure with the conventional EL device, i.e., the bottom-emission structure. High performance, such as 50 and 40% increases in efficiency and brightness, respectively, was achieved. This enhanced EL performance was attributed to the structural change in the EL device, leading to reduced optical loss and enhanced electric field applied to the phosphor.

Enhanced Optical and Electrical Properties of Inorganic Electroluminescent Devices Using the Top-Emission Structure

Enhanced Optical and Electrical Properties of Inorganic Electroluminescent Devices Using the Top-Emission Structure

Front-Light Source Using Inverted Organic Light-Emitting Diodes with Microcathode Arrays

We have demonstrated an organic light-emitting diode (OLED) front-light source with a blinding microcathode array on a transparent electrode and a top-emission structure. Contrast ratio was improved by inserting MoO3 at the indium–tin-oxide (ITO)/Al interface. In a device of glass substrate/ITO/MoO3/meshed Al/lithium fluoride (LiF)/tris(8-hydroxyquinolinato) aluminum(III) (Alq3)/bis[N-(1-naphthyl)-N-phenyl] benzidine (α-NPD)/MoO3/semitransparent Au structure, the maximum luminance of top-side emission was 1,140 cd/m2, and the contrast ratio was 19:1. The transmittance was 44% at 555 nm.

22.3: New Full Color OLEDs Technology Based on Advanced Color Conversion Method Using Ink‐Jet Printing

AbstractIn this paper, we describe the development of advanced color conversion method for full‐color AMOLED displays. Ink‐jet printing technique is innovated for processing color conversion materials to demonstrate 2.8″ full‐color a‐Si AMOLED display prototypes. They perform high efficiency with 100% NTSC gamut ratio and wide viewing angle, employing anode‐common top emission structure.

54.4: 4.1 inch Top-Emission AMOLED on Flexible Metal Foil

We have developed a 4.1 inch AMOLED display with top emission structure on stainless steel foil. The p-channel TFTs on metal foil exhibited the field-effect mobility of 75.1 cm2/Vs, threshold voltage of −3.9V, and subthreshold swing of 0.9V/dec. Active-matrix back planes were fabricated with the poly-Si TFT with a conventional pixel circuit consisting of 2 TFTs and 1 cap. The scan driver circuits with PMOS were integrated on the metal foil.

38.2: 302-ppi High-Resolution AMOLED using Laser-Induced Thermal Imaging

Samsung SDI has developed 2.6-inch full color VGA Active Matrix Organic Light-Emitting Diode (AMOLED) display with the world's highest resolution of 302ppi using Laser Induced Thermal Imaging (LITI) method with the top emission structure. A voltage compensating pixel circuit with 2μm design-rule in low-temperature poly-Si (LTPS) thin film transistors (TFTs) was introduced to compensate the variation of the threshold voltage (Vth) in order to improve the image quality. Moreover, an aperture ratio of ∼40% was obtained for each pixel even though the sub-pixel pitch was 28um. The luminance for the white color was 200cd/m2 and color gamut was 74% compared to national television standard committee (NTSC) standards. These results show the possibility of high-resolution AMOLED display incorporating the LTPS technology and LITI method for digital mobile era applications in the near future.

51.2: A. 4.3‐in. VGA (188 ppi) AMOLED Display with a New Driving Method

AbstractWe developed a 4.3‐inch VGA driver‐integrated AM‐OLED display with the world's highest pixel density of 188ppi by using high performance TFTs, a top emission structure, a technology for improving the precision of mask alignment in OLED deposition by RGB emitter's selective deposition method, and a 4Tr/Cell digital time‐gray‐scale driving method which improves image quality by fixing the gate potential of driving TFT.

9.2: A 5.0‐in WVGA AMOLED Display for PDAs

AbstractSamsung SDI has developed a full color 5.0″ WVGA AMOLED display using top emission structure with a super fine pitch of 0.1365 mm 186 ppi, the world's highest density OLED display ever reported to date. Scan driver circuits and demux circuits were integrated within the display panel, using low temperature poly‐Si TFT CMOS technologies, and data driver circuits were mounted using COG IC. Peak luminescence was greater than 300 cd/ with power consumption of 500 mW with 30% of the pixels on.