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In recent years, the active-matrix organic light-emitting diode (AMOLED) displays have been greatly required. A voltage compensation pixel circuit based on an amorphous indium gallium zinc oxide thin-film transistor is presented for AMOLED displays. The circuit is composed of five transistors–two capacitors (5T2C) in combination with an OLED. In the circuit, the threshold voltages of both the transistor and the OLED are extracted simultaneously in the threshold voltage extraction stage, and the mobility-related discharge voltage is generated in the data input stage. The circuit not only can compensate the electrical characteristics variation, i.e., the threshold voltage variation and mobility variation, but also can compensate the OLED degradation. Furthermore, the circuit can prevent the OLED flicker, and can achieve the wide data voltage range. The circuit simulation results show that the OLED current error rates (CERs) are lower than 3.89% when the transistor's threshold voltage variation is ±0.5V, lower than 3.49% when the mobility variation is ±30%. [ABSTRACT FROM AUTHOR]

In recent years, the active-matrix organic light-emitting diode (AMOLED) displays have been greatly required. A voltage compensation pixel circuit based on an amorphous indium gallium zinc oxide thin-film transistor is presented for AMOLED displays. The circuit is composed of five transistors–two capacitors (5T2C) in combination with an OLED. In the circuit, the threshold voltages of both the transistor and the OLED are extracted simultaneously in the threshold voltage extraction stage, and the mobility-related discharge voltage is generated in the data input stage. The circuit not only can compensate the electrical characteristics variation, i.e., the threshold voltage variation and mobility variation, but also can compensate the OLED degradation. Furthermore, the circuit can prevent the OLED flicker, and can achieve the wide data voltage range. The circuit simulation results show that the OLED current error rates (CERs) are lower than 3.89% when the transistor’s threshold voltage variation is ±0.5V, lower than 3.49% when the mobility variation is ±30%.

We show how three-dimensions kinetic Monte Carlo simulations can be used to carry out an operational lifetime study of thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs) and to deduce the sensitivity to various degradation scenarios. The approach is demonstrated for an experimentally well-characterized efficient green-emitting device. The simulation workflow includes an equilibration phase, an equilibrated pristine state phase and a degradation phase. Acceleration of the simulations by extrapolation from simulations at large current densities makes the simulation time realistically feasible. Such a procedure is also often followed in experimental studies. Degradation is assumed to be triggered by exciton-polaron quenching and exciton-exciton annihilation processes. A comparison of the simulated and experimental time-dependence of the luminance decay provides the probability that a degradation-triggering event leads to the formation of a degraded molecule. For the TADF OLED that has been studied, this parameter is only weakly dependent on the assumed scenario, provided that the degraded molecules are assumed to form trap sites, and is found to be ∼(0.2−0.7)×10−9. The approach is expected to enable systematic in silico studies of the operational lifetime and its sensitivity to the material composition, layer structure, charge carrier balance, and the use of refined device principles such as hyperfluorescence.

Aging is still the most challenging issue for organic light‐emitting diodes (OLEDs), which causes the image‐sticking artifacts on active‐matrix organic light‐emitting diode (AMOLED) displays and limits their lifetime. To overcome this demerit, an aging model is necessary to compensate for aging artifacts. In this paper, we present a unified OLED aging model, which combines three feasible modeling approaches of OLED degradation, namely, data‐counting, electro‐optical, and correlation methods. The model can be used to predict the efficiency decay of OLED pixels during operation. It mitigates weaknesses and limitations of each of these three models and deploys their strengths, respectively. In the first aging stage, the data‐counting model is prioritized, and in the later stages, it is calibrated using the correlation model. The dependency of the efficiency decay on the operation point of OLED is covered by the electro‐optical model. The unified model is based on both phenomenal and physical effects. It delivers more reliability to determine an OLED's degradation over a long‐term operation and a wide operation range like current amplitude and/or temperature range. The unified aging model applies to either an analog or a digital driving scheme. A corresponding compensation based on the aging model can be applied for extending the AMOLED lifetime. [ABSTRACT FROM AUTHOR]

Irreversible chemical reactions are responsible for limited operational lifetime of organic light‐emitting devices (OLEDs). These reactions are triggered by highly reactive polaron pairs present in the emissive layer of OLEDs. Fast recombination of the polaron pairs is, therefore, crucial for slow degradation and high stability of OLED materials. Here, a study of the formation and annihilation of close polaron pairs in binary mixtures of wide bandgap hosts and a series of blue‐phosphorescent Ir(III) complex dopants, including two novel compounds, is reported. OLED devices containing doped light‐emitting layer are fabricated, and their operational lifetimes are estimated. Although inaccessible in solid films, charge recombination kinetics inside the polaron pairs is measured in liquid solutions using nanosecond laser flash photolysis. Multiscale computer simulations are applied to connect experimental results in different media and predict recombination rates in the device, with proper account taken of the inner‐ and outersphere reorganization in nonpolar materials. Predicted rates correlate with measured operational lifetimes, which demonstrates the key role of polaron pairs in the OLED degradation process. The developed methodology is useful for the rational design of novel OLED materials with higher efficiency and stability. [ABSTRACT FROM AUTHOR]

It is a proposal for preventing image sticking of OLED using deep learning based object detection. It was able to detect transparent objects superimposed on complex backgrounds and we got 92% detection performance. The burn‐in pixels can be detected in real time and the luminance can be adjusted to 80%. [ABSTRACT FROM AUTHOR]

A voltage-programmed pixel circuit based on low-temperature poly-silicon (LTPS) thin-film transistors (TFTs) is presented for active-matrix organic light-emitting diode (AMOLED) displays. The circuit consists of six p-type transistors and one capacitor (6T1C). During the extraction stage, the circuit extracts the driving TFT's threshold voltage and the power supply voltage. During the data input stage, the circuit generates a charging voltage, which is associated with the driving TFT's mobility and the OLED's threshold voltage. Consequently, the pixel circuit, using only one capacitor, compensates not only for the TFT's electrical characteristics variations, i.e., the threshold voltage variation and mobility variation, but also for the power supply voltage drop and the OLED degradation. The circuit simulation results reveal that the OLED current error rates (CERs) are lower than 5.09% when the threshold voltage varies by ± 0. 5 V , lower than 3.61% when the mobility varies by ± 30 % , and lower than 9.16% when the voltage drop varies by − 0. 5 V in the data voltage range. [ABSTRACT FROM AUTHOR]

Design and synthesis of novel mono- and dimeric quinazoline derivatives (+)-6-methyl-6-pyridin-2-yl-5,6-dihydrobenzo[4,5]imidazo[1,2- c ]quinazoline ( 1 ) and (+)-6-[(6-methyl-5,6-dihydrobenzo-[4,5]imidazo[1,2-c]quinazolin-6-yl)-pyridin-2-yl]-6-methyl-5,6-dihydro-benzo-[4,5]imidazo-[1,2- c ]quinazoline ( 2 ) have been described. Both 1 and 2 have been characterized by elemental analyses, FT-IR, 1 H and 13 C NMR, HRMS spectroscopic studies and their structures authenticated by X-ray single crystal analyses. Photophysical properties of these compounds have been studied by UV/VIS absorption and fluorescence spectroscopy and transient photoluminescence analysis in solution, powder, and non-doped (neat) and doped vacuum-deposited films. A broad emission spectrum spanning most of the visible range and good thermal stability indicated promising application of 1 and 2 as OLED emitters. Unfortunately, under current flow we observed rapid device degradation, presumably to be related to free –N H moiety in these compounds. [ABSTRACT FROM AUTHOR]

An active matrix organic light emitting diode (AMOLED) display driver IC, enabling real-time thin-film transistor (TFT) nonuniformity compensation, is presented with a hybrid driving method to satisfy fast driving speed, high TFT current accuracy, and a high aperture ratio. The proposed hybrid column-driver IC drives a mobile UHD $\left({{3840} \times {2160}} \right) AMOLED panel, with one horizontal time of 7.7\,\upmu \texts at a scan frequency of 60 Hz, simultaneously senses the TFT current for back-end TFT variation compensation. Due to external compensation, a simple 3T1C pixel circuit is employed in each pixel. Accurate current sensing and high panel noise immunity is guaranteed by a proposed current-sensing circuit. By reusing the hybrid column-driver circuitries, the driver embodies an 8 bit current-mode ADC to measure OLED V–$I$ transfer characteristic for OLED luminance-degradation compensation. Measurement results show that the hybrid driving method reduces the maximum current error between two emulated TFTs with a 60 mV threshold voltage difference under 1 gray-level error of 0.94 gray level (37 nA) in 8 bit gray scales from 12.82 gray level (501 nA). The circuit-reused current-mode ADC achieves 0.56 LSB DNL and 0.75 LSB INL. [ABSTRACT FROM PUBLISHER]

Abstract: Alq3 has been the reference material used widely in the fabrication and characterization of efficient OLEDs due to its good properties as electroluminescent and electron transporting layer. Although the inclusion of these devices in commercial displays and lighting devices represents many benefits, the knowledge about the progressive loss of performance and efficiency with time for such devices is still limited. Therefore, it is an incentive to understand the mechanisms of Alq3 degradation when it is subjected to the influence of various extrinsic factors such as UV radiation. In the present work the degradation processes of Alq3 thin films as a result of 254nm UV light irradiation are presented and discussed. The degradation products produced by the action of UV light were evaluated by time-of-flight mass spectrometry using electron stimulated ion desorption and laser desorption ionization techniques. Strong evidence for carboxylic acid formation after photodegradation was observed by the electron desorption technique. [Copyright &y& Elsevier]

This paper proposes a new pixel circuit for an active matrix organic light-emitting diode (OLED) display, which consists of five thin-film transistors (TFTs) and one capacitor. This circuit develops techniques of pulsed drive and reverse bias to achieve desired emitted brightness levels and elongate OLED life times, respectively. A current mirror is also adopted in the circuit to minimize emission nonuniformity of the OLED panel. The required input data voltages for varied displayed gray levels are calculated based on analytically known TFT and OLED models and the designed circuit architecture. The designed pixel circuit is simulated with realistic TFT models for validating expected performance to realize 256 gray levels and minimizing nonuniformity. The designed circuit is implemented in a 2.4-in quarter video graphics array panel, which shows favorable performance for minimizing display nonuniformity and alleviating OLED degradation. In addition, a closeness is clearly observed among analytical predictions, simulations, and experimental measurements. [ABSTRACT FROM AUTHOR]

Abstract: This work demonstrates the feasibility of a novel pixel circuit by using three a-Si:H TFTs. The proposed circuit can stabilize the OLED current and provide an additional driving current to ameliorate the brightness degradation of the AMOLED. Measurement results indicate that the current degradation of the proposed circuit, caused by VTH variations, is less than 5% over more than 50,000s at 60°C, whereas that of a conventional 2T1C pixel circuit is larger than 34%. Furthermore, to ameliorate the decrease in luminance owing to the OLED degradation, the OLED current can be increased by 10% by analyzing the current degradation and modulating the detected voltage appropriately. [Copyright &y& Elsevier]

This paper describes how a reversed-bias voltage affects organic light-emitting diodes (OLEDs) with green emitting \Alq3:C545T (40 nm). The luminance efficiency and the active area of the test OLED devices are 8–11 cd/A and 2.5 mm \times 2.5 mm, respectively. The OLED lifetime under an ac driving scheme can be apparently improved, in contrast with that under a dc driving scheme. Experimental results indicate that adjusting the duty ratio of the ac driving scheme can ameliorate the brightness uniformity; meanwhile, the normalized luminance of a 20% duty ratio after a 3600-s stress is 94.3%, and that of dc stress is 76.4%. Therefore, a novel pixel circuit with three p-type thin-film transistors (TFTs) for an active-matrix OLED application is proposed to ameliorate the brightness uniformity. Variations of the threshold voltage of the driving TFT are compensated for, and the performance and lifetime of the OLED are improved by using an ac driving method. Simulation results indicate that the output current is almost constant over the data range. Furthermore, the current error rate of the proposed pixel circuit is less than 6.5%. [ABSTRACT FROM AUTHOR]

This study presents a novel voltage-modulated pixel circuit for active-matrix organic light-emitting diode (AMOLED) consisting of five n-type thin-film transistors (TFTs), one additional control signal, and one storage capacitor. The proposed circuit, which can be implemented in all-n-type and all-p-type low temperature poly-silicon (LTPS) TFT technologies, successfully compensates for threshold voltage deviation of TFTs and facilitates correction of OLED degradation using a voltage feedback method. Simulation and experimental results for all-n-type TFTs indicate that the proposed pixel circuit reduced the nonuniformity brightness problem effectively by compensating for threshold voltage variation in TFTs and reduced the degradation of emission efficiency in OLEDs. [ABSTRACT FROM PUBLISHER]

In this letter, we propose a compensation method for organic light-emitting diode (OLED) degradation occurring in a digital driving scheme for active-matrix OLED displays. The proposed method, in which we are the first to propose, employs the modified stretched exponential decay (SED) model to characterize the OLED degradation and compensates for the associated luminance decrease; the lifetime of an OLED panel can thereby be extended. The OLED panel is fabricated using low-temperature poly-Si thin-film transistors, and measured to verify the modified SED model and the proposed compensation method. The measurement results show that the luminance degradation with and without the proposed method is 0.3% and 6%, 4% and 17.8%, and 7.4% and 30.4%, for red, green, and blue OLEDs, respectively. This measurement is taken after 40 h of operation under a 350 cd/ \mathrmm^\mathrm \mathbf 2 initial luminance. Accordingly, the proposed compensation method extends the lifetime of the OLED panel up to 72.5, 15.5, and 20.75 times longer in red, green, and blue OLEDs, respectively, compared with the conventional method. [ABSTRACT FROM AUTHOR]

This work presents a new pixel circuit using low‐temperature polycrystalline‐oxide thin‐film transistors (LTPO TFT) for active‐matrix organic light‐emitting diode (AMOLED) displays. The proposed circuit can compensate for the threshold voltage (Vth) variations of driving TFT. Moreover, the degradation of OLED can be reduced to a certain degree. The simulation results demonstrate that the current of OLED is independent of the Vth shifting and changes as the OLED threshold voltage. That means this LTPO circuit can improve the stability of displays. [ABSTRACT FROM AUTHOR]