Organic Light-emitting Diode Panel Research Articles

Measurement of inkjet droplet speed using interference fringe by diffracted light

Inkjet printers are key technologies in manufacturing organic light-emitting diodes and quantum dot light-emitting diode panels, but precise measurement and control of inkjet droplets remains challenging. The international standard, IEC 62899-302-1, uses shadow image-based measurement with high magnification microscopes to observe picoliter-sized droplets. However, high magnification lens results in a shallow depth of field or narrow optimal measurement area, causing the blurring image if the droplet does not pass through the optimal measurement area. To solve this, we propose using the interference image-based measurement with interference fringe patterns by inkjet droplets as a tool to measure the flight speed of droplets. The interference fringe patterns can be obtained simply passing the droplet through within the light beam path, providing approximately 1000× wider measurement area compared to the shadow image-based measurement, making it practical to use in the industry. The flight speed of droplets analyzed with the interference image-based measurement at various frequencies and amplitudes of the inkjet driving voltage were compared with the shadow image-based measurement. The interference image-based measurement showed a coefficient of variation of less than 3%, showing higher repeatability than the shadow image-based measurements.

Modulation of Intermolecular Interactions in Organic Emitters for Highly Efficient Organic Light-Emitting Diodes.

The adverse aggregated-caused quenching (ACQ) problem of most electroluminescent materials existing in highly doped thin films is one of the key factors impeding the commercialization of high-efficiency organic light-emitting diodes (OLEDs) panel. Whereas, by delicately constructing and modulating moderate intermolecular interactions, some aggregates have been demonstrated to present distinct luminescent properties such as tunable emission spectra, improved photoluminescence quantum yields, different emission mechanism and enhanced horizontal transition dipole ratio (Θ) of emitting layer, providing feasible solution for ACQ problem. The luminescence from newly generated emissive state in aggregates is different from the traditional "isolated" molecules in organic electronics and will possess novel properties and applications. Herein, we summarize the different types of intermolecular interactions within emitter aggregates exhibiting distinct luminescent mechanisms, as well as their effects on photoluminescent and electroluminescent properties, offering reliable reference for the advancement of highly efficient OLEDs utilizing aggregated emitters.

Ultraviolet light blocking optically clear adhesives for foldable displays via highly efficient visible-light curing

In developing an organic light-emitting diode (OLED) panel for a foldable smartphone (specifically, a color filter on encapsulation) aimed at reducing power consumption, the use of a new optically clear adhesive (OCA) that blocks UV light was crucial. However, the incorporation of a UV-blocking agent within the OCA presented a challenge, as it restricted the traditional UV-curing methods commonly used in the manufacturing process. Although a visible-light curing technique for producing UV-blocking OCA was proposed, its slow curing speed posed a barrier to commercialization. Our study introduces a highly efficient photo-initiating system (PIS) for the rapid production of UV-blocking OCAs utilizing visible light. We have carefully selected the photocatalyst (PC) to minimize electron and energy transfer to UV-blocking agents and have chosen co-initiators that allow for faster electron transfer and more rapid PC regeneration compared to previously established amine-based co-initiators. This advancement enabled a tenfold increase in the production speed of UV-blocking OCAs, while maintaining their essential protective, transparent, and flexible properties. When applied to OLED devices, this OCA demonstrated UV protection, suggesting its potential for broader application in the safeguarding of various smart devices.

Chemical Reactivities and Organic Light-emitting Diode Properties of some Polyaromatic Molecules

High-performance organic-light emitting diode (OLED) display panels have been very popular lately due to their many advantages compared to liquid-crystal display (LCD) and light-emitting diode (LED) panels. It is also well known that the materials used in OLED panels are important in determining OLED performance. Starting with the selection of materials which have rich π-electrons will be a good start for the design of high-performance OLED materials. For this aim, the OLED properties of some cyclic aromatic structures with rich π-electrons such as 2,2ꞌ-bi-1,6-naphthyridine (BNP), 1,6-bis(4ꞌ-pyridine)-2,5-diazahexane (BPDH), 3,3ꞌ-bis[3-(2-pyridyl)pyrazol-1-yl]biphenyl (BPPB), 5,5ꞌ-dicyano-2,2ꞌ-bipyridine (DCBP), 2,2ꞌ-dimethyl-4,4ꞌ-bipyrimidine (DMBP), and 4ꞌ-phenyl-2,2ꞌ:6ꞌ2ꞌꞌterpyridine (Ph-TERPY) were theoretically analyzed using computational chemistry tools. The calculations of monomeric and dimeric structures of mentioned molecules were carried out at B3LYP/6-31G(d) and B3LYP/TZP levels, respectively. The OLED properties of the investigated compound were explained by means of OLED parameters such as the reorganization energies, adiabatic-vertical ionization potentials and adiabatic-vertical electron affinities, the effective transfer integrals, and the charge transfer ratios. In the light of computational chemistry, it is indicated that these studied molecules will be utilized in which layers of OLED device. In addition to OLED analysis, in the light of the calculated reactivity descriptors, the chemical reactivities of the studied molecules were discussed.

Artificial intelligence-assisted auto-optical inspection toward the stain detection of an organic light-emitting diode panel at the backplane fabrication step

This paper attempts to implement an auto-optical inspection (AOI) system using artificial intelligence (AI) technology for cost reduction in the production of organic light emitting diode (OLED) panels, specifically at the production stage of the thin film transistor (TFT) . Further, to improve the accuracy of mura detection, the possible causes of mura were properly identified, and a model to control and predict mura occurrence was realized based on the sufficient analysis of these causes. More specifically, an explainable AI (XAI) prediction model was developed using the fab image and test element group (TEG) engineering methods, which could be applied as input data for the circuit simulations to improve the accuracy of the overall simulations. Initially, we attempted to predict backplane stain using only the TFT width, length dimension, and resistance–capacitance (RC) extraction data, but the results were not accurate. Consequently, we identified, via sufficient analysis, that the correlation between the dehydrogenation and stain, and introduced an AI model. As a result, the accuracy was improved from 50 to 80%, which is more effective in terms of time and cost, compared to conventional simulation through the TCAD analysis. Overall, by implementing the inspection method described in this paper, it was possible to detect stains at the backplane stage, which was only possible during the final test stage, thereby resulting in significant cost savings.

Visible-Light-Curable Acrylic Resins toward UV-Light-Blocking Adhesives for Foldable Displays.

Current technological advances in the organic light-emitting diode panel design of foldable smartphones demand advanced adhesives with UV-blocking abilities, beyond their conventional roles of bonding objects and relieving deformation stress. However, optically clear adhesives (OCAs) with UV-blocking ability cannot be prepared using conventional UV-curing methods relying on a photoinitiator. Herein, a new acrylic resin that can be efficiently cured using visible light without oxygen removal is presented, which may be used to develop UV-blocking OCAs for use in current flexible displays. A novel photocatalyst and a specific combination of additives facilitate sufficiently rapid curing under visible light in the presence of UV-absorbers. Only a very small amount of the highly active photocatalyst is required to prepare UV-blocking OCA films with very high transparency in the visible region. Using this system, a UV-blocking OCA that nearly meets the specifications of an OCA used in commercialized foldable smartphones is realized. This technology can also be utilized in other applications that require highly efficient visible light curing, such as optically clear resins, dental resins, and 3D/4D-printable materials.

Mechanical simulation for the bending process of the AMOLED panel pad

Panel pad bending is a critical process to improve the screen-to-body ratio of an active-matrix organic light-emitting diode (AMOLED) panel. The failure analysis of the metal wirings is the key to ensure the reliability of signal transmission when the pad be bent to the back of the panel. In the present work, the sub-modeling technique combined with the periodic boundary condition was used to simulate the stress distribution of the bending area of the pad. The progressive failure of bent metal wirings was investigated by the extended finite element method. It is proved to be rational to prevent the wirings damage if the interlayer dielectric is replaced by an organic layer. In order to reduce stress of metal wirings, it is a measure to replace the original ultraviolet (UV) curable adhesive with a higher-modulus UV adhesive. The simulated results also show that rectangular perforations can avoid the stress concentration caused by the holes compared with circular perforations. For better stress distribution of metal wirings, it is necessary to increase the lengths of the rectangular holes and decrease the widths of that to a certain extent, which is helpful for restraining crack propagation by means of low-stress zones and holes.

Effect of Interlayer Stress on U Bends and Water Droplet Bends

The interlayer stress (IS) analysis of the flexible active-matrix organic light-emitting diode (AMOLED) panel is critical for decreasing the stress concentration and reducing the risk of overall screen failure. This article relies on the linear elastic models of ABAQUS to simulate finite element analysis of foldable panels. This article discussed three sensitive locations of the flexible AMOLED panel caused by two different bending methods including U bends and water droplet bends. The finite element method for simulating the layer analysis was constructed to analyze the effect of optically clear adhesive (OCA) film thickness on the distribution of stress and strain. The module can be optimized by changing the thickness and shear modulus of OCA. With the decrease of OCA thickness and the increase of stiffness, the maximum stress of the organic light-emitting diode (OLED) layer is decreased by 20% which is 55 Mpa; meanwhile, the IS of the entire module is reduced by about 30%.

P‐133: Enhancement of Light‐Emitting Efficiency Through Impurity Controls by Using Prep‐NMR Technique

An electroluminescence (EL) material plays a key role in electrical and optical efficiency of an organic light emitting diode (OLED) display. High purity, over 99.9%, EL materials have been required to be deposited onto OLED panel, producing a long‐life time device. Even less than 0.1% of impurities are deposited on the panel, which can drop their efficiency and lifetimes very seriously. In this work, we have developed faster and more accurate evaluation methods to identify unknown impurities in emitting materials. We can separate each other by using semi‐prep liquid chromatography and define their chemical structures by combining mass spectrometry and nuclear magnetic resonance results. The impurities in the in the manufacturing process were identified, which causes the efficiency drop, down to 8%. We find out these were coming from other EL materials in the process by accident. Finally, we can guarantee highquality assurance of our panels and eliminate potential risk factors in the manufacturing process.

45‐3: Effects of Near‐UV Irradiation on Organic Light‐emitting Diodes and Their Solutions Using UV Blocking Layer

The organic light‐emitting diode (OLED) panels showed a significant color change in the solar radiation evaluation. After exposure to solar radiation, the luminance of some OLEDs was significantly decreased. In these OLEDs, the purity of electron transport layer (ETL) material was noticeably decreased after light exposure. It was determined that some gasses came out from the pixel‐define layer (PDL) by measuring the thermal desorption spectroscopy (TDS). By these gasses, the degradation was accelerated in organic layers and cathode. When the solar radiation evaluation was done with putting the 420 nm cut‐off filter on the panel, the color variation was absolutely disappeared. We paid attention to this result that the problem was solved by blocking a near‐UV light. A new capping layer (CPL) material increasing the absorption of near‐UV light was used. While the solar radiation evaluation was passed, they had very small process margin on evaporation of red and green interlayer. Moreover, color difference of white light was increased. When a near‐UV light absorbing dye was inserted to the polarizer film, color change in the solar radiation evaluation absolutely disappeared. Finally, we could pass the solar radiation evaluation through this attempt and the OLED panels with this polarizer film applied to mass production.

7‐3: OLED Camera‐Under Panels with Improved Imaging Quality

In this paper, we report the novel design and fabrication of OLED (organic light‐emitting diode) Camera‐under panels (CUP) with improved transmittance and imaging quality. We utilized TFT (thin film transistor)‐outside structure and patterned cathode in the CUP region. The diffraction simulation, transmittance test, Point spreading function (PSF) test, and scene photos proved the efficiency of our solution. Remarkable enhancement of imaging performance, which was identical to that of a normal AA‐hole OLED panel, was achieved. The results confirm the effectiveness of our CUP design strategy and also the potential of our design to be commercially used in the industry.

IEEE Open Journal of the Solid-State Circuits Society Special Section on Integrated Circuits and Systems Based on Thin-Film Transistors

Thin-Film transistors (TFTs) are ubiquitous today as a backplane technology for various display and imager products. Those transistors act as switches in active-matrix liquid-crystal displays (AM-LCDs) or as full-pixel engines, including driving and threshold compensation, in active-matrix organic light-emitting diodes (AM-OLEDs) panels. TFT manufacturing requires only a limited amount of photolithographic steps, making it a relatively simple transistor technology, compared to the traditional Si CMOS technologies. The processing temperature of TFT technologies is sufficiently low to be compatible with glass and can even enable flexible substrates. Finally, these transistors have been developed specifically for large-area applications, such as televisions and X-ray scanners. Consequently, the backplane size for TFTs has evolved from the generation-1 glass panel of 270 mm by 360 mm to generation-10.5, which is manufactured on a glass panel of 2.94 m <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times3.37$ </tex-math></inline-formula> m <xref ref-type="bibr" rid="ref1" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[1]</xref> . This is profoundly different from traditional Si CMOS integrated circuits, which are fabricated nowadays on 200 mm or 300 mm round wafers. The critical dimension of the TFT technology on glass or flexible substrate in production is in the range of a few micrometers. The TFT research in the display field focuses on enabling increasingly better pixel resolution, improved visual quality, larger panels for LED walls, flexible displays, camera-behind display, sensor integration, and many more.

Analysis and simulation of reddish overshoot in active matrix organic light-emitting diode display with varying p-doped hole transport layer concentrations

A typical organic light-emitting diode (OLED) display has common organic layers between adjacent pixels, which ensure ease of manufacturing process and efficiency in operation. The p-doped hole transport layer (p-HTL) has low electrical resistivity, which results in a high efficiency OLED. However, the low resistivity results in various side effects, including color crosstalk and overshoot, mainly due to lateral leakage current flowing through this layer. Furthermore, virtual reality and augmented reality devices that require extremely high pixels per inch (PPI) and superior image quality are very sensitive to lateral leakage current. In this study, we propose a passive driving panel based on RGB top emission to efficiently measure and model the lateral leakage current characteristics according to the p-HTL concentration. In addition, we constructed a 1.5-inch active matrix organic light-emitting diode panel based on the n-type low-temperature polycrystalline silicon 4T2C pixel circuit. Subsequently, we quantitatively analyzed the reddish overshoot phenomenon during the black to white image transition. This effect was reduced at p-HTL concentrations under 1%. Finally, we analyzed the overshoot mechanism through SPICE simulations and realized the optimal lateral resistance value of the common organic layer for each PPI. • Passive driving OLED and AMOLED display with varying p-HTL concentration. • Effect of the lateral leakage current on the AMOLED display. • Analysis of reddish overshoot mechanism through SPICE simulations and accurate OLED modeling. • An optimal lateral resistance value for the common organic layer is proposed for each PPI.

Optimization of lamination process for flexible display using OCR

Due to the recent development of different types of flexible displays, the lamination process for bonding between the organic light-emitting diode (OLED) panel and the window cover has become more important. In this study, we studied the process technology that can be applied to various types of displays by applying the pattern lamination process method using optically clear resin(OCR) instead of the existing optically clear adhesive (OCA). The OCR pattern was optimized by adding dam pattern during the process, and the overflow was within 0.1 mm and the thickness deviation was within 10%. Using the optimized process method, OCR with various viscosities could be used to optimize the process.

Positioning Error Limit for the Last Droplet Deposition into a Microcavity in the Manufacture of Printed OLEDs.

In the manufacture of the emissive layer and the encapsulation layer of organic light-emitting diode panels, inkjet printing has the advantages of high material utilization, low cost, flexibility in patterning, and large-area production. Especially for emissive layer printing, the micro-pixel array brings a higher requirement of droplet positioning accuracy and volume of the liquid in a pixel. To achieve a uniform deposit morphology, several droplets are usually needed in the inkjet printing of emissive layers. As the printing process continues, these droplets coalesce, and its equilibrium outcome can be roughly approximated by a section of an ellipsoidal cap under the interaction of the surface tension and gravity. The existence of the "ellipsoidal cap" enlarges the spread, and the maximum allowable out-of-pixel spreading length is decreased because of the "ellipsoidal cap" in the neighboring pixel. In this research, the volume of fluid method is used to study the behavior of the last droplet deposition into the wetted microcavity. The effects of wettability, droplet deposition speed, and initial volume of the liquid in the pixel on the printable region are investigated, and printing parameter spaces that result in successful printing are established.

An electrically switchable dye-doped liquid crystal polarizer for organic light emitting-diode displays

A conventional polarizer for an organic light-emitting diode (OLED) display deteriorates light efficiency by blocking more than 50% of the emitted light from the OLED. The use of such a polarizer with a quarter-waveplate is inevitable to achieve an excellent dark state because it blocks the reflection of incoming ambient light to the OLED. However, when there is no incoming light outside of the display, the polarizer does not play a role of suppressing the reflection but sacrifices emitted light. In this study, we propose a switchable dye-doped liquid crystal (DDLC) that serves as a polarizer for strong ambient light in the voltage-off state, which effectively absorbs ambient light reflection from OLED electrodes. With the DDLC in the voltage-on state, it can be switched to a non-absorption state for weak ambient light, allowing the emitted light from the OLED to pass through it, which enhances the light efficiency of the OLED. Consequently, the switchable DDLC performs effectively in terms of display contrast ratio and light efficiency for any ambient light conditions. The 2 wt% DDLC polarizer not only exhibits a smaller reflectance than that of a conventional polarizer, but also improves the emission intensity by 61%. Our proposed DDLC polarizer can be compactly equipped with an OLED panel and can improve the lifetime of the device by enhancing optical efficiency.

Modified distributed Bragg reflector for protecting organic light-emitting diode displays against ultraviolet light.

Sunlight/UV (ultraviolet)-induced degradation is still a critical issue for outdoor applications of organic light-emitting diode (OLED) displays. Therefore, effective UV-blocking structures that can prevent OLED displays from sunlight/UV degradation and still keep the OLED panels' display performance is necessary. In this report, modified distributed Bragg reflector (DBR) structures having UV-absorbing dielectric materials and adjusted layer/pair thicknesses were developed to realize effective UV blocking properties (nearly 0% transmittance below 400 nm), constantly high transmittance like glass in the visible range (∼92%) required for display applications, and sharp transition in transmission between the UV and the visible ranges. Furthermore, under the rigorous IEC 60068-2-5 solar test condition, it was verified that the developed modified, UV-blocking DBR can effectively enhance the OLED panel's resistance against UV/solar-induced degradation, effectively reducing voltage shifts of OLED devices after repeated solar test cycles.

A high image quality organic light‐emitting diode display with motion blur reduction for ultrahigh resolution and premium TVs

AbstractIn this paper, we present a high image quality organic light‐emitting diode (OLED) display with motion blur reduction technology. Our latest work includes driving method that reduces motion blur using an adaptive black data insertion, brightness compensation technology, the simple structure pixel with low capacitance coupling for horizontal noise, and the multifunction integrated gate driver. The moving picture response time (MPRT) value of the OLED display panel with a fast response time was significantly affected by the frame frequency and the compensation driving method. The MPRT value of the large‐size OLED display panels was significantly decreased by using the integrated gate driver circuit with an MPRT reduction method. The decrease in the MPRT value originated from the turning of the emitting pixels off in advance resulting from providing black data. The integrated gate drivers were designed to achieve the normal display, the black data insertion, and the compensation mode. The MPRT value of the 65‐in. ultrahigh‐definition (UHD) OLED panels was decreased to 3.4 ms by using an integrated gate driver circuit. The motion blur of large‐size OLED display panels was significantly reduced due to a decrease in the MPRT value.

A study on the effect of the vertical sound field control of the flat panel display speaker on audience

Technological improvement in the display industry, the organic light-emitting diode(OLED) panel manufacturer changed the quality of picture and sound improvement. In previous research, we introduced the technology that uses the display panel as a speaker and also to improve the sound quality by improving the vibration characteristics and horizontal acoustic characteristics of an OLED panel. In this study, we analyzed the characteristics of the vertical direction sound of the TV and to consider auditory sense at various distances. When watching TV, unlike normal viewers, the infant and child viewers are too close to the screen. Acoustic transmission using conventional TV allows the reflected sound to propagate from downward. So, near the TV and in a low position, a loud sound is formed. This causes hearing damage at close range and low clarity at long range. The exciter speakers can basically eliminate these disadvantages of the sound field. And, by adaptive control of the sound, it is possible to transmit a clear sound in a wide space by reducing loss due to the distance. This paper introduces the results of the study on the improvement of sound quality through control algorithm and the protection of hearing audiences through sound field analysis.Technological improvement in the display industry, the organic light-emitting diode(OLED) panel manufacturer changed the quality of picture and sound improvement. In previous research, we introduced the technology that uses the display panel as a speaker and also to improve the sound quality by improving the vibration characteristics and horizontal acoustic characteristics of an OLED panel. In this study, we analyzed the characteristics of the vertical direction sound of the TV and to consider auditory sense at various distances. When watching TV, unlike normal viewers, the infant and child viewers are too close to the screen. Acoustic transmission using conventional TV allows the reflected sound to propagate from downward. So, near the TV and in a low position, a loud sound is formed. This causes hearing damage at close range and low clarity at long range. The exciter speakers can basically eliminate these disadvantages of the sound field. And, by adaptive control of the sound, it is possible to transmit...

Do users perceive the same image differently? Comparison of OLED and LCD in mobile HMDs and smartphones

ABSTRACTThe two leading panel types in the current smartphone market are OLED (organic light-emitting diode) and LCD (liquid crystal display). Even though OLED is known to show more vivid and brighter colors, however, LCD is still dominant in the market. In the rising era of HMDs (head-mounted displays), the present study examined which panel the consumers prefer in the smartphone and HMD context by investigating the characteristics of panels as perceived by the consumers as well as the consumers’ VR (virtual reality) material preferences. The characteristics of the different panels as perceived by the consumers were extracted, and the users’ VR material preferences were ranked. The study findings indicate that OLED should be used for HMDs to increase the consumers’ satisfaction. Furthermore, the users did not find any significant difference between the two different luminance values of the OLED panel that was used for the study, which indicates that the luminance of the panel can be optimized for a comfortable and satisfying HMD viewing setting.