Organic Light-emitting Diode Display Research Articles

Tetraborated Intrinsically Axial Chiral Multi-resonance Thermally Activated Delayed Fluorescence Materials.

Chiral multi-resonance thermally activated delayed fluorescence (CP-MR-TADF) materials hold promise for circularly polarized organic light-emitting diode (CP-OLED) and 3D display. Herein, we present two pairs of tetraborated intrinsically axial CP-MR-TADF materials, R/S-BDBF-BOH and R/S-BDBT-BOH, with conjugation-extended bidibenzo[b,d]furan and bidibenzo[b,d]thiophene as chiral sources, which effectively participate in the distribution of frontier molecular orbitals. Due to the heavy-atom effect, sulfur atoms are introduced to accelerate the reverse intersystem crossing process and increase efficiency of molecules. R/S-BDBF-BOH and R/S-BDBT-BOH manifest ultra-pure blue emission peaking at 458/459 nm with full width at half maximum of 27 nm (0.16 eV), photoluminescence quantum yields of 90%/91% and dissymmetry factors (|gPL|) of 6.8 × 10-4/8.5 × 10-4, respectively. Correspondingly, the CP-OLEDs exhibit good performances with external quantum efficiency of 30.1% and |gEL| factors of 1.2 × 10-3.

Compressed-SDR to HDR Video Reconstruction.

The new generation of organic light emitting diode display is designed to enable the high dynamic range (HDR), going beyond the standard dynamic range (SDR) supported by the traditional display devices. However, a large quantity of videos are still of SDR format. Further, most pre-existing videos are compressed at varying degrees for minimizing the storage and traffic flow demands. To enable movie-going experience on new generation devices, converting the compressed SDR videos to the HDR format (i.e., compressed-SDR to HDR conversion) is in great demands. The key challenge with this new problem is how to solve the intrinsic many-to-many mapping issue. However, without constraining the solution space or simply imitating the inverse camera imaging pipeline in stages, existing SDR-to-HDR methods can not formulate the HDR video generation process explicitly. Besides, they ignore the fact that videos are often compressed. To address these challenges, in this work we propose a novel imaging knowledge-inspired parallel networks (termed as KPNet) for compressed-SDR to HDR (CSDR-to-HDR) video reconstruction. KPNet has two key designs: Knowledge-Inspired Block (KIB) and Information Fusion Module (IFM). Concretely, mathematically formulated using some priors with compressed videos, our conversion from a CSDR-to-HDR video reconstruction is conceptually divided into four synergistic parts: reducing compression artifacts, recovering missing details, adjusting imaging parameters, and reducing image noise. We approximate this process by a compact KIB. To capture richer details, we learn HDR representations with a set of KIBs connected in parallel and fused with the IFM. Extensive evaluations show that our KPNet achieves superior performance over the state-of-the-art methods.

Research of aging test on high Tg colorless polyimide

AbstractFor the past few years, colorless polyimide (CPI) has been drawn much attention for its application in transparent electronics. The high temperature (even to 450°C) process of the preparation of organic light‐emitting diode display (OLED) device may have huge challenges on the properties of CPI, so we designed a series of aging test experiments to study the influence of test temperature and atmosphere on the high transparency percentages (Tr%) of CPI films with structure of Glass/SiO2/CPI/SiO2. As the aging temperature increased from 430 to 450°C and then to 470°C, the Tr% of the film decreased significantly. Comparing with the sample without aging, the transmission losses were 0.22%, 1.42%, and 4.82% for the films aging with 430, 450, and 470°C in N2 atmosphere, respectively. Additionally, aging in nitrogen resulted in less Tr% loss (1.22%) compared with air (1.42%). This research offers insights into how to maintain the high Tr% of CPI films during high‐temperature processing. Furthermore, it supports the development of more durable and reliable CPI‐based components for OLED displays and other transparent electronic devices. This can lead to advancements in the performance of these devices, potentially extending their lifespan and broadening their range of applications.

A simple fabrication method of passive-matrix organic light-emitting diode display without a photolithography process

A passive-matrix organic light-emitting diode (PMOLED) display was fabricated in a simple self-aligned imprint lithography (SAIL) method without utilizing a photolithography process. This SAIL method is a top-down fabrication process in which all layers constituting the PMOLED are deposited in advance and only the necessary parts are removed by plasma etching to fabricate the display. As an etch mask for sequential plasma etching, a three-dimensional resin structure in which all patterns are pre-aligned was formed using an imprint process. PMOLED fabrication by this SAIL process has the advantage of being very simple as it consists of only one imprint and sequential plasma etching processes. In the PMOLED with 400 pixels fabricated, all pixels operated without deterioration of OLED performance during the fabrication process.

Enhancement of light extraction and out-coupling efficiency of thin: film stacked organic light-emitting diode display

Enhancement of light extraction and out-coupling efficiency of thin: film stacked organic light-emitting diode display

A novel ultra large size organic light emitting diode display for premium televisions

AbstractIn this paper, we present novel ultra large size organic light emitting diode (OLED) display technologies with high image quality for premium televisions (TVs) using an advanced coplanar oxide thin film transistor (TFT) backplane, microlens array (MLA)‐based OLED, small size gate driver in panel for narrow bezel, and pixel charging enhancement method with external compensation. Using these technologies, we improved the luminance efficiency about 20% and reduced the integrated gate driver design area to 40%. We have achieved the life time of the gate driver in panel longer than 100,000 h in reliability test. The pixel charging ratio is more than 80% in all gray levels. Using the developed OLED display, we have successfully developed up to ultra large size 88‐in. 8K and 97‐in. 4K OLED TVs.

High‐performance, coplanar amorphous InGaZnO thin‐film transistors by spray pyrolysis on polyimide substrate for low‐cost manufacturing of foldable active‐matrix organic light emitting diode display

AbstractWe report a method for low‐cost deposition of bubble‐free, high‐quality amorphous InGaZnO (a‐IGZO) on polyimide (PI) substrate for foldable active‐matrix organic light emitting diode (AMOLED) display by spray pyrolysis. The coplanar thin‐film transistor (TFT) with spray‐pyrolyzed (SP) a‐IGZO on PI substrate exhibits threshold voltage (VTH) of −0.8 V, saturation mobility of 40.95 cm2 V−1 s−1, and subthreshold swing of 0.18 V per decade with on/off drain current ratio of ~108. The high mobility TFT could be achieved using high substrate temperature (350°C) and low contact resistance by NF3 plasma on the SP a‐IGZO. The TFT shows a ΔVTH of −0.4 V when it is bent on a cylinder of 1‐mm radius. The TFT shows the ΔVTH of +0.05 V for positive bias temperature stress at +20 V at 60°C for 1 h. The ring oscillator made of a‐IGZO TFTs exhibits an oscillation frequency of 2.38 MHz at VDD of 10 V with a propagation delay of 9.13 ns per stage. Therefore, the a‐IGZO TFT by spray pyrolysis could be used for low‐cost, high‐performance, and flexible display TFT backplane.

P‐1.1: User‐behavior based External Compensation for Active‐Matrix Organic Light Emitting Diode Displays

Various compensation methods, including external and internal compensation method, have been proposed to solve the non‐uniformity of degradation between different array pixels. Current commercial methods can be summarized as Edge‐side self‐compensation method, which has not fully utilized the information of user behavior to provide the optimized compensation method for specific user and will result in the waste of resources. In this paper, we propose a user‐behavior based external compensation (UBEC) method to provide customized compensation method for customers. A simulation based on MATLAB platform is designed to verify the proposed method. The simulation results on three different App usage scenarios proved the performance of UBEC method. The resources consumed for sensing the operating status can be greatly saved with UBEC method.

Sustainable use of organic light-emitting diode (OLED) and liquid crystal display (LCD) glass wastes as cement replacement in concrete

With the persistently increasing use of electronic and display devices, there has been a significant surge in OLED and LCD glass wastes. One way to efficiently utilize such wastes is incorporating them in mortars or concrete as supplementary cementing material (SCM) by replacing a part of cement. The use of SCMs is customary in contemporary concretes. Different industrial by-products and waste materials have been investigated earlier for such applications. In this paper, the use of OLED and LCD glass wastes as a partial replacement for cement binders has been reviewed. Mechanical properties, durability attributes, microstructural characteristics, and structural performance of the cementitious composites incorporating LCD and OLED powders have been assessed. It has been concluded that adding LCD and OLED leads to improved mechanical strength after 28-day age. The modified composites have better durability, enhanced microstructure, lower porosity, and superior overall performance. The enhanced mechanical and durability properties with LCD and OLED addition is attributed to the pozzolanic activity due to high amounts of alumina and amorphous silica. Incorporating LCD and OLED wastes in concrete as a partial cement replacement can also reduce environmental burden and concrete cost, thus promoting sustainable development.

A New Pixel Circuit Compensating for a Decrease in Luminance of the Stretchable Active Matrix Organic Light Emitting Diode Display

The stretchable display is a next-generation flexible display because it is possible to implement free-form with free change, and various studies are being conducted. The most likely display technology for implementing a stretchable display is the organic light emitting diode (OLED), which is suitable for forming on flexible substrates because it can emit light on its own without using the back light unit (BLU). In addition, through advantages such as high contrast ratio, fast response time, and wide viewing angle, OLED is applied from small size panels such as mobile to large size panels such as televisions. Thin film transistor, a device applied to drive active matrix of OLED, is represented by the amorphous silicon (a-Si), low temperature poly silicon (LTPS), and oxide TFT such as amorphous In-Ga-Zn-oxide(a-IGZO). The a-IGZO, which has advantages such as high filed effect mobility and low leakage current compared to a-Si:H, is used as a backplane of commercial OLED panels. In addition, it is suitable for application to flexible substrates due to low process temperature, and high transmittance in the visible area due to band gap energy of about 3.1 eV can be applied to transparent display. In research to minimize damage to TFTs or OLEDs when the area of flexible substrates increases, rigid island structures protect devices from damage by forming rigid structures on soft substrates. Devices protected from damage caused by increasing the area can maintain performance, and each pixel can maintain brightness. However, when the area of the panel is increasing, the gap between the pixels increases, which leads to a decrease in the luminance of the panel. Among the studies to compensate for the decrease in brightness by increasing the area of the stretchable display, Kang et al. proposed a stretchable pixel circuit for AMOLED displays, which compensates for the reduced luminance by bootstrapping. The proposed circuit increases luminance through a variable capacitor with a strain-dependent capacity change. However, compensation for TFT's threshold voltage and voltage drop, which are possible causes of luminance reduction in OLED were not considered. The threshold voltage or power voltage of a different drive TFT for each pixel affects the current supplied from the backplane to the OLED electrode, and the current supplied differently for each pixel affects the light intensity of the OLED device, so compensation should be considered. In this study, we propose a novel pixel circuit consisting of seven n-type transistors and two capacitors. In order to evaluate the compensation ability of the proposed pixel circuit, a simulation using the RPI Level = 35 model was conducted. Fig. 1 (a) shows the simulation result of the output current of the proposed pixel circuit by the change in the capacitance of C2. Before the capacitance of C2 increased, the output current was 7.65 μA, but when the capacitance of C2 increased by 10%, the output current increased by 2.22% to 7.82 μA, and when the capacitance of C2 increased by 4.31%.Figure 2 (b) shows the output current caused by the change in VDD voltage of the proposed pixel circuit and the conventional pixel circuit. As the VDD of the conventional pixel circuit changed by 3.0 V, the output current decreased by 40.90% from 8.02 μA to 4.74 μA. In the case of proposed pixel circuit, output current decreased by 21.83% from 7.65 μA to 5.98 μA as VDD changed by 3 V, and decreased by 0.77% to 7.60 μA when VDD changed by 1.1 V. Figure 3 shows the output current due to the threshold voltage change of TFT in the proposed pixel circuit and conventional pixel circuit. In the conventional pixel circuit, output current changed from 10.13 μA to 5.53 μA as the threshold voltage of TFT changed by 3 V. In the proposed pixel circuit, output current changed from 7.12 μA to 6.45 μA with a 3 V change in the threshold voltage. As a result of the simulation, the proposed pixel circuit can compensate for luminance change by an increased area, voltage drop, and the threshold voltage shift of the TFT. Figure 1

A compact polymer\u2013inorganic hybrid gas barrier nanolayer for flexible organic light-emitting diode displays

Atomic layer infiltration technology allows the formation of a nanometer-thick polymer-inorganic hybrid barrier layer in polymer material for flexible organic light-emitting diode (OLED) displays. In this study, according to transmission electron microscopy and secondary-ion mass spectrometry analysis results under various process conditions, a compact polymer-inorganic hybrid nanolayer was successfully formed in a polymer and good barrier performance was revealed with a low water vapor transmission rate under optimal process conditions. Additionally, through gas chromatography-mass spectrometry measurements after ultra-violet radiation testing, polymer out-gassing decreased compared to bare polymers. Based on barrier properties, the polymer with a polymer-inorganic hybrid barrier nanolayer was applied to a flexible OLED display as a substrate. During storage tests and folding tests, the flexible OLED display exhibits good reliability and better flexibility compared to those with an inorganic barrier layer. These results confirm that the polymer-inorganic hybrid nanolayer is suitable for barrier layer formation in flexible OLED displays.

Hydration characteristics and microstructure evolution of concrete with blended binders from LCD and OLED wastes

The use of pozzolanic waste materials as partial cement replacement is customary in contemporary concretes from the sustainability perspective. In this study, glass wastes from organic light-emitting diode (OLED) and liquid crystal display (LCD) were used waste as supplementary cementing material (SCM) in concrete. For the first time, detailed microstructural and hydration attributes have been studied for such blended concretes. Concretes with 10%, 20%, and 30% substitution of ordinary Portland cement (OPC) by OLED and LCD glass powders were developed. The resulting mechanical properties, hydration attributes, and microstructural features were studied at various ages, up to one year. Superior mechanical properties were shown after 28-day age for blended concretes; however, much profound improvement in compressive and flexural strength was observed at 1-year age. The enhanced mechanical properties of modified concretes are attributed to greater pozzolanic activity and secondary hydrates formation of OLED and LCD glass powders in alkaline cementitious matrix. Greater C-S-H gel formation, lower permeability, and more refined microstructure of the blended concrete were corroborated by thermogravimetric analysis (TGA), Rietveld quantitative phase analysis (RQPA), backscattered electron image analysis (BSE), and mercury intrusion porosimetry (MIP). 20 wt% has been found as the optimal value of cement replacement by either LCD or OLED powder. The results clearly indicate LCD and OLED can be successfully used as SCM for developing concrete with improved properties.

Firmware-based Capacitor and Equivalent Series Resistance (ESR) Meter

This paper presents the development of a capacitor ESR meter, which covers capacitance and ESR measurements as well as the interrelationship of the constituent parts/circuits. The idea is to keep the hardware design simple, transferring the complexity to firmware which controls the hardware. In particular, it uses automatic functions controlled by relays thus there is no need for switches and its automatic calibration ensures there is no need for menus. This work covers voltmeter function, C/R time constant function and ESR function using Arduino Uno boards. Each firmware code was developed one after the other, starting with the voltmeter function then C/R time constant function and finally ESR function. Results were checked by serial data transfer from Arduino Uno board to the laptop that is running the Arduino compiler with terminal. One Arduino Nano interface was constructed to interface the project shield. The firmware was developed to provide the voltmeter function, C/R time constant function and ESR function. An organic light-emitting diode (OLED) display was used to show measurement results. Logic control was added to provide the required functions to work as intended, as well as an automatic short circuit detection at DUT terminals firmware which includes a calibration cycle. Conventional ESR meters are usually have complex hardware, in contrast the design presented in this work shifts the focus to the firmware so that hardware is uncomplicated. This reduces the cost that typically comes with more hardware components. Keywords : Capacitor, ESR Meter, C-R Time Constant, Arduino, OLED Display, Calibration DOI: 10.7176/CEIS/13-1-02 Publication date: January 31 st 2022

A Low Cost and Nondestructive Micro-Pocket Meter on Chlorophyll Contents of Vegetable Leaves

Highlights A meter on the contents of chlorophyll a and b and total chlorophyll of vegetable leaves was developed. Three LEDs as light sources and a light sensor to sense transmitted light through leaves. The models to predict the chlorophyll contents were established using multiple linear regression. The pocket detector makes chlorophyll content detection easy, fast, and in situ. Abstract. Detecting the contents of chlorophyll (chlorophyll a, chlorophyll b) is important to instruct vegetable growth. However, the traditional spectrophotometry used in measuring these contents requires expensive equipment, is destructive, time-consuming, toxic (acetone), and unable to measure in situ. To make the detection nondestructive, quick, cheap, safe, and on-site, a low-cost micro-pocket photosynthetic chlorophyll content meter was developed in this study. The meter consisted of a micro-controller of STC12C5A60S2, three light-emitting diodes at 460, 660, and 980 nm, a digital light sensor, three keys, one organic light-emitting diode display, and a power supply unit. The software was developed by using the C language. The leaves of leaf lettuce, garden sass, and spinach were used as samples. The models used to predict the contents of chlorophyll a, chlorophyll b, and total chlorophyll, as well as SPAD values, were established based on the absorbance of vegetable leaves at three wavelengths by using the multiple linear regression method. The root-mean-squares errors of the developed meter for chlorophyll a, chlorophyll b, total chlorophyll, and SPAD value were 0.068 mg/g, 0.024 mg/g, 0.085 mg/g, and 1.7, respectively. The meter was small in size and low in cost. The contents of chlorophyll a, chlorophyll b, total chlorophyll, and SPAD value, could be given in 2 s. Keywords: Absorbance, Chlorophyll a, Chlorophyll b, Chlorophyll content, Pocket meter, SPAD.

Blue Light Intensity in Organic Light-Emitting Diode and Liquid-Crystal Display Televisions

Exposure to artificial blue light from screens, especially at evening or nighttime hours, can suppress melatonin production, throw the circadian rhythm off balance, and lead to general difficulty falling asleep. This study sought to investigate the difference in blue light intensity in organic light-emitting diode (OLED) and liquid-crystal display (LCD) screens, specifically in the form of televisions. An observational and quasi-experimental method was used, using a photometer to measure light intensity and a longpass optical filter to block out light ranging from 415 to 515 nanometers, serving as the wavelength of blue light for this study. Two televisions—one OLED and one LCD—were used, with five colors being displayed on each one, one at a time. The LCD television contained more relative blue light than the OLED television for four out of the five colors displayed. On average for all colors, the LCD television emitted 24.92% more blue light than the OLED television, relative to their overall brightnesses. Limitations in scope and the potential of confounding variables interfering with data prevent any definitive conclusions from being drawn, however this study still contributes to the current body of knowledge with evidence towards a trend of lessened blue light intensity in OLED screens compared to LCD screens, which correlates with speculation by other researchers. This study sets the ground for future research investigating the potential of OLED technology in lowering exposure to blue light, thus lessening the negative impacts it can have on individuals.

Programmable illumination smartphone microscopy (PISM): A multimodal imaging platform for biomedical applications

Microscopes on the smartphone platform are handy for a wide range of applications. We report herein a programmable illumination smartphone microscopy (PISM) as a flexible multimodal imaging platform for contrast enhancement of various samples using different low-cost consumer optoelectronics parts. A miniature (0.96 inches), programmable organic light-emitting diode (OLED) display has been used as an optical source to develop the proposed PISM system. By displaying different color and binary patterns on the OLED display, six well-established imaging modes, namely bright-field (BF), dark-field (DF), oblique illumination (OI), Fluorescence imaging (FI), Rheinberg illumination (RI), and differential phase contrast (DPC) imaging have been demonstrated on a single optical setup. Furthermore, by incorporating additional optical components such as an optical polarizer into the setup, another imaging mode-polarized imaging has been realized with the proposed PISM system. The optical resolution of the designed platform is found to be 1.7 µm and delivers an acceptably resolvable image in all modalities. The versatility of the PISM has been demonstrated through imaging several specimens that include micro-beads, human epithelial check cells (HECC), starch, fungus specimen, nerve tissue cells, and red blood cells.

A device to detect leakage at the patient end of total intravenous anaesthesia

The use of total intravenous anaesthesia (TIVA) is limited by concerns of disconnections of the tubing, resulting in accidental awareness. We designed a sensor device to detect leakages at the patient end and notify the medical personnel, thereby allowing immediate intervention in preventing awareness. For moisture detection, resistive sensing was selected as the working principle. The prototype was in proximity to the tubing from the TIVA pump and the patient’s intravenous cannula, and able to detect leakages in all potential leakage sites and activate an alarm. Our device consists of a disposable bandage (sensor), attached to a reusable clamp that is directly coupled to a central module (SparkFun MicroView, a small microcontroller with built-in Organic Light-Emitting Diode (OLED) display). The disposable bandage is wrapped around the possible leakage sites. Crucially, the disposable bandage is integrated with two separate moisture sensing threads. When moisture is present, the central module detects a drop in resistance across the moisture sensing threads and activates a flashing LED and buzzer. We have successfully created a functional leak detection device, comprising a moisture sensing bandage and an audio and visual alert system, to address the problem of undetected TIVA leakages at the patient end.

Color mismatch and observer metamerism between conventional liquid crystal displays and organic light emitting diode displays, Part II: Adjacent stimuli with a larger field of view

In part I of this study [Opt. Express 29, 12292 (2021)10.1364/OE.418675], 50 human observers matched the color appearance of six color stimuli produced by four smartphone displays, including one conventional liquid crystal display (LCD) and three organic light emitting diode (OLED) displays, to those produced by a reference smartphone OLED display. The matching and reference stimuli had a field of view (FOV) around 4.77° and were 5.72° apart. In this experiment, we carefully designed and built a new apparatus to make the two stimuli adjacent to each other with an FOV around 20.2°. This not only made the viewing condition in the experiment similar to the typical viewing condition of smartphone displays, but also allowed for an easier color matching, resulting in smaller intra- and inter-observer variations. The performance of the four CMFs, however, were not significantly changed with the increase of the FOV. The CIE 2006 2° CMFs still had the best performance in characterizing the color matches, which did not support the recommendation of using 10° CMFs for stimuli with an FOV beyond 4°. Meanwhile, for the pairs of stimuli with matched color appearance, the LCD display always had the greatest chromaticity differences and degrees of observer metamerism among the four displays, regardless of the CMFs. In particular, the chromaticities of the stimuli produced by the LCD display were always shifted towards the -u’+v’ direction in the CIE 1976 u’v’ chromaticity diagram, when calculated using the CIE 1931 CMFs. This implies that the neutral colors shown on LCD displays would have a yellow-green tint on OLED displays, if they were calibrated to the same chromaticities using the CIE 1931 2° CMFs.

Optimizing the display performance for virtual reality systems

We propose a systematic optimization method for two commonly used display devices, organic light-emitting diode (OLED) display and liquid crystal display (LCD), for virtual reality (VR) headsets. An optical simulation model for the VR system is established, and three performance metrics, namely total light efficiency (TLE), field color gamut coverage, and field color non-uniformity, are proposed as the optimization objectives. For the RGB (red, green, and blue) OLED display, the microcavity structure is optimized to suppress the field color unevenness while maintaining a high TLE and large field color gamut coverage. For the direct-lit LCD, the optimization is from the viewpoint of entire VR system. A two-dimensional patterned prism film is implemented in the backlight unit to locally modulate the radiation pattern of the LCD. Thus, the vignetting effect in the VR system is alleviated and the TLE is further enhanced by 40%. After optimizing the OLED display and LCD, their pros and cons in the VR systems are analyzed. Our optimization method is proven to be effective for designing a proper display panel for VR systems.

A New Pixel Circuit Compensating for Strain-Induced Luminance Reduction in Stretchable Active-Matrix Organic Light Emitting Diode Displays

A new compensation pixel circuit is proposed for a stretchable active-matrix organic light-emitting diode (AMOLED) display. The proposed pixel circuit utilizes a double-gate structure driving thin-film transistor (TFT) and a capacitive strain sensor to compensate for the change in TFT threshold voltage and luminance reduction due to display deformation. Simulation results showed that the current error rate as a result of threshold voltage variation was less than 6.5%, even under a 15% strain. Also, the current error due to luminance reduction was reduced significantly under the 15% strain at all gray levels.