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In this work, we studied the thermal behavior and addressed the challenges of life testing of large area OLED devices. In particular, we developed an indirect method to accurately calculate the life time of large-area OLED lighting panels without physically life-testing the panels. Using small area OLEDs with structures identical with the tested pa...
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... white PHOLED architecture used in this study contains only six organic layers including two emissive layers for red-green and light blue emission [4]. Figure 1a shows a photo image of a 19.11 cm 2 white PHOLED panel and Figure 1b shows the IR image of the panel driven at 4,000 cd/m 2 (equivalent to a luminous emittance of 10,000 lm/m 2 ) after reaching ther- mal equilibrium. The ambient temperature was maintained at 18°C during the IR im- aging. ...
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... white PHOLED architecture used in this study contains only six organic layers including two emissive layers for red-green and light blue emission [4]. Figure 1a shows a photo image of a 19.11 cm 2 white PHOLED panel and Figure 1b shows the IR image of the panel driven at 4,000 cd/m 2 (equivalent to a luminous emittance of 10,000 lm/m 2 ) after reaching ther- mal equilibrium. The ambient temperature was maintained at 18°C during the IR im- aging. ...
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... includes a 1.5 times efficacy enhancement achieved by adding a light extraction block. As can be seen from the IR image in Figure 1b, the maximum operational temperature of the panel is less than 22°C, which is only 4°C above the ambient environment. ...
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... further validate this prediction, we life-tested an OLED panel at room temperature (20°C) at J = 10 mA/cm 2 so as to compare the measured LT80 with the above prediction. The life-test curve of the OLED panel driven at J = 10 mA/cm 2 is shown in Figure 10. Also included for comparison is the life-test curve for the equivalent pixel at the same current density. ...
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... luminance for the large-area panel was calibrated for total light emission by measurement before and after life test inside a 20" integrating sphere. Figure 10 shows that the measured lifetime of the large-area OLED light panel at 10 mA/cm 2 is LT80 = 512 hrs. This value agrees very well with our indirect prediction of LT80 = 526 hrs. ...
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... Device protection against oxygen and moisture at high humidity levels (e.g., 85 RH) can be ensured by employing advanced thin-film encapsulation methods, 22 but the thermal stability of an LED system depends on both intrinsic and modified charge transport characteristics in the functional charge transport layers 23 as well as exciton relaxation dynamics in the emissive layer (EML). Several studies have been published previously on the temperature-dependent electroluminescence (EL) performance of organic LEDs (OLEDs), [24][25][26] perovskite LEDs, 27,28 and QLEDs [29][30][31] . As the focus of the present work, for example, M. Zhang et al. investigated both photoluminescence (PL) and EL performance of their red QLEDs within a 120-300 K temperature range but did not carry out their experiments at temperatures higher than room temperature (RT). ...
The aerobic and thermal stability of quantum-dot light-emitting diodes (QLEDs) is an important factor for the practical applications of these devices under harsh environmental conditions. In this paper, we demonstrate all-solution-processed amber QLEDs with an external quantum efficiency (EQE) of >14% with almost negligible efficiency roll-off (droop) and a peak brightness of >600,000 cd/m2, unprecedented for QLEDs fabricated under ambient air conditions. We investigate the device efficiency and brightness level at a temperature range between -10 C to 85 C in a 5-step cooling/heating cycle. Unlike previous studies reported in the literature, we conducted the experiments at relatively high brightness levels, required for outdoor lighting applications. The results reveal that the device performance increases slightly at sub-zero temperatures (-10 C) and drops slightly at very high temperatures (85 C), proving acceptable thermal stability. Overall, the performance parameters do not change dramatically over the temperature range within the experimental uncertainty range. Interestingly, the device efficiency parameters recover to the initial values upon returning to room temperature. The variations in the performance are correlated with the modification of charge transport characteristics and induced radiative/non-radiative exciton relaxation dynamics at different temperatures. Being complementary to previous studies on the subject, the present work is expected to shed light on the potential feasibility of realizing aerobic-stable ultrabright droop-free QLEDs and encourage further research for solid-state lighting applications.
... O RGANIC light emitting diodes (OLED belong to SSL-Solid State Lighting family) have developed rapidly since the turn of the century and are likely to become standard lighting devices in the future thanks to their high-performance, excellent quality of light, a lifespan of over 10000 hours , having thin panels as well as being flexible or transparent when needed. Although, in comparison to typical LEDs, OLED panels operate at a lower power density for the same light output [1], their lifetime is shorter due to the presence of organic materials, meaning their degradation is faster than semiconductor LEDs. Several papers have studied OLED degradation by measuring different features, such as luminance [2], brightness, IV characteristics [3], forward voltage [4] etc. Ultimately, destructive methods can also be used to understand the degradation mechanism of the OLED, by peeling off the cathode layer for example [5]. ...
Luminance is the main feature indicating OLED degradation; however this requires delicate photometric measurements that are difcult and costly to realize in-situ. In this paper, an original luminance decay prediction method not requiring optical measurements will be presented. Analysis of the impedance revealed a strong correlation between the luminance and the time constant of the equivalent circuit. As a result, the time constant is chosen as the main feature to track OLED degradation, the evolution of which is linearly modelled over time at different stress levels using the design of experiments (DoE) methodology. Simultaneously, a linear relationship between luminance degradation and the evolution of time constants, in terms of the thermal stress applied, enables prediction of the luminance degradation over time. This method is an accurate novel solution for luminance tracking in particular for data taken inside the experimental plan limits.
... Because of the energy is uniformly applied over a large area, the temperature rise during operation is relatively small. Thus, OLEDs produce an efficient heat dissipation as compared to the inorganic LEDs [11][12]. To date, OLEDs have captured a substantial interest from the worldwide lighting and display industries including Philips, Osram, GE Lighting, Panasonic, Novaled, Mitsubishi and many other companies [13][14][15][16]. ...
Due to its thin geometry, the luminance output of an OLED can be profoundly affected by the presence of unwanted charge due to capacitance effect. Thus, the optimum discharge time is necessarily crucial to be identified, so that the occurrence of the surplus charge can be fully terminated. However, studies on the discharge time of OLED were occasionally reported, indicated that this issue remains unexplored. Therefore, the objective of this paper was to study the effect of discharge time on luminance output of OLED. In this study, the on/off cycles approach was employed by which the OLED samples were switched-on (Ton) and-off (Toff) at specific times. With constant voltage and current supply, the Ton was fixed at 1 s, whereas the Toff were validated at 1 s, 10 s, 20 s, 30 s and 40 s. The stability of luminance output was captured by using a chroma-meter, carried out in an in-house black-box. The optimum discharged time was found at Toff 40 s and the results demonstrated that the luminance output was mostly dependent on the discharge time. The attained data emphasized the significance of determining the optimum discharge time of OLED to ensure the luminance output is accurate and reliable.
https://jamt.utem.edu.my/jamt/article/view/6013
... Inorganic LEDs have the widest temperature range. OLED displays function well in freezing cold environments and age fast if heated 114,115 . LCDs respond slowly in cold weather, and the upper limit depends on the clearing temperature (T c ). ...
Presently, liquid crystal displays (LCDs) and organic light-emitting diode (OLED) displays are two dominant flat panel display technologies. Recently, inorganic mini-LEDs (mLEDs) and micro-LEDs (μLEDs) have emerged by significantly enhancing the dynamic range of LCDs or as sunlight readable emissive displays. “mLED, OLED, or μLED: who wins?” is a heated debatable question. In this review, we conduct a comprehensive analysis on the material properties, device structures, and performance of mLED/μLED/OLED emissive displays and mLED backlit LCDs. We evaluate the power consumption and ambient contrast ratio of each display in depth and systematically compare the motion picture response time, dynamic range, and adaptability to flexible/transparent displays. The pros and cons of mLED, OLED, and μLED displays are analysed, and their future perspectives are discussed. Mini and micro light-emitting diodes (LEDs) could move to the centre-stage of display screen technologies once they mature. Shin-Tson Wu of the University of Central Florida and colleagues analysed the pros, cons, and future prospects of the latest display screen technologies, especially for use in smartphones, smart watches, virtual and augmented reality, and heads-up vehicle displays. These applications require bright, flexible, transparent, and power-efficient displays. The currently dominant liquid crystal displays (LCDs) require a backlight unit, dictating their shape and flexibility. LCDs with a backlight unit made from mini LEDs are becoming rapid contenders to the conventional technology. So are displays using organic light-emitting diodes, but these are limited in their brightness and lifespans. Emissive displays made from mini and micro-LEDs show huge potential once manufacturing costs can be brought down.
... Inorganic LEDs have the widest temperature range. OLED displays function well in freezing cold environments and age fast if heated 114,115 . LCDs respond slowly in cold weather, and the upper limit depends on the clearing temperature (T c ). ...
Micro-LED (light-emitting diode) is a potentially disruptive display technology, while power consumption is a critical issue for all display devices. In this paper, we develop a physical model to evaluate the power consumption of micro-LED displays under different ambient lighting conditions. Both power efficiency and ambient reflectance are investigated in two types of full color display structures: red/green/blue (RGB) micro-LEDs, and blue-LED pumped quantum dots color-conversion. For each type of display with uniform RGB chip size, our simulation results indicate that there exists an optimal LED chip size, which leads to 30–40% power saving. We then extend our model to analyze different RGB chip sizes, and find that with optimized chip sizes an additional 12% average power saving can be achieved over that with uniform chip size.
... In most cases, the distributions parameters include an acceleration factor. Still, the authors of [17] refused to work with accelerated tests, claiming that the degradation mechanism is not the same under accelerated and normal conditions. They proposed another degradation sign, the temperature of the junction. ...
Modeling the lifespan of OLED (Organic Light-Emitting Diode) is a complex task as it depends on different - potentially interacting factors. As the literature on this subject is still scant, new parametric models for calculating the lifespan of OLED are proposed in this work. The Design of Experiment (DoE) methodology is used for cost and accuracy reasons. Different lifespan models based on thermal and electrical experimental aging tests are proposed. As stress factors, current density, temperature and their interactions, which are rarely taken into account in aging studies are simultaneously involved. The analysis of the model parameters highlights the prevalence of temperature compared to current density on the luminance performance of OLEDs. Non-linear models appear as the most accurate.
... The improvement of the metal mesh design can achieve good uniformity, but the OLED is a current driving device, and the metal mesh is always resistant, so the metal mesh in the emitting area of the WOLED panel always has non-negligent power dissipation and leads to reliability problems, such as the short between anode and cathode [15], and the thermal problems of the organic materials [16]. ...
... The entire device structure is as follows ( Figure 1 to reduce the non-uniformity of the WOLED panel, such as using a tandem structure that can reduce the resistance of the OLED device and improve the uniformity of the WOLED panel [13], and using a different type of grid design by, say, improving the shape, width, and length of the metal mesh to improve the uniformity and emitting area of the WOLED panel [14]. The improvement of the metal mesh design can achieve good uniformity, but the OLED is a current driving device, and the metal mesh is always resistant, so the metal mesh in the emitting area of the WOLED panel always has non-negligent power dissipation and leads to reliability problems, such as the short between anode and cathode [15], and the thermal problems of the organic materials [16]. ...
A novel OLED (organic light emitting diode) lighting panel, which uses a special layout design, can reduce the photolithography cycles and process costs and is more reliable. It only needs two steps of photolithography cycles, which include an ITO (InSnO compound transparent oxide) pattern and insulator pattern. There is no need for the metal bus pattern of the ordinary design. The OLED device structure is a type of red-green-blue (RGB)-stacked emitting layer that has a good color index and greater adjustability, which improves the performance of the device. This novel design has the same equipment and material requirement compared to the ordinary design, and it is very beneficial in terms of high volume and low-cost production. It uses a hyper driving method because the entire OLED lighting panel is divided into many sub-emitting units; if one of the sub-emitting units is burned out, it has no effect on the adjacent sub-emitting unit, so the reliability is markedly better than the ordinary design.
... Numerous experimental studies have been conducted to date to assess the reliability of solid-state lighting, mostly through accelerated testing (ALT) [3]- [5]. The goal of ALT is to estimate the nominal lifetime of OLEDs when subjected to normal usage conditions that would be expected in service [6]. ...
... As discussed earlier, the AF for degradation of OLEDs are the operating temperature and driving current (or initial luminance intensity) [28], [29]. First, the AF for initial luminance intensity has an inverse power relationship [3], [4], [10]. The acceleration factor (AF lum ) for initial luminance intensity between the usage condition and the stress level is expressed by ...
... where L d and I lumd are the lifespan and the initial luminance intensity under the normal usage conditions, respectively; L a and I luma are the lifetime and initial luminance intensity under the accelerated loading conditions, respectively. Another acceleration factor for temperature (AF temp ) is expressed by [3]: ...
Despite advantages of organic light-emitting diode (OLED) displays over liquid crystal displays, reliability concerns persist. These concerns must be addressed before OLED displays are widely adopted. In particular, existing methods are unable to reliably estimate the lifetime of large OLED displays (i.e., displays of 55 inches or larger). This study proposes a novel model that incorporates physical and statistical uncertainty to estimate the lifetime of large OLED panels under normal usage conditions. A likelihood-ratio-based validation method is presented to determine the validity of the calculated model parameters. A bi-variate acceleration model with two critical factors – temperature and luminance – is presented. The lifespan predicted by the proposed lifetime model shows a good agreement with the experimental results.
... In addition, when the temperature increases, the energy required for electron-hole recombination is lower, and consequently, a lower forward voltage is necessary to drive the OLED [16], [24]. Regarding the OLED aging, the operation under high temperatures causes a reduction in the produced luminous flux, and consequently, the device lifetime decreases [17], [25]. ...
This paper presents a new theoretical equivalent model (TEM) for organic light-emitting diodes (OLEDs). The parameters of TEM are identified using a simple characterization procedure based on auxiliary circuits and low-cost equipment. From this TEM, a method for intrinsic capacitance identification is proposed. This model is useful to simulate and analyze OLED devices considering dynamic and steady-state operation conditions. In addition, it provides guidelines for manufacturers and lighting designers to enhance the device performance and to design dedicated OLED drivers. In order to validate the proposal of this paper, four commercial OLEDs are tested, and the comparison between the theoretical and the experimental results is satisfactory.
The efficiency improvement of organic light-emitting diodes (OLEDs) is important but challenging. Here, we introduce a unique OLED with a hole modulation layer (HML) in the middle of its emission layer (EML). The external quantum efficiency and power efficiency can be improved by approximately 58% when an HML with optimized thickness is inserted. HML insertion can efficiently retard hole flow, thus improving (i) exciton distribution uniformity and (ii) local electron–hole charge balance. A systematic study of the individual contributions of two EMLs separated by the HML shows that the former factor dominantly works at low current densities (< 10 mA/cm2), whereas the latter factor functions over the entire current density range of the OLED. Therefore, the efficiency improvement is greatest at low current densities, which aligns with the typical operating range in display applications. The results provide a deeper understanding of the OLED emission mechanism, and the proposed OLED structure can significantly benefit high-performance OLED displays.Graphical Abstract
