OLED Lifetime Research Articles

Influence of Exciton-Polaron Quenching Occurring at the Interface Mixing Zone on the Operational Lifetime of Solution-Processed OLED

Influence of Exciton-Polaron Quenching Occurring at the Interface Mixing Zone on the Operational Lifetime of Solution-Processed OLED

31.2: Invited Paper: Advanced Materials Development for Ink‐Jet Printed OLEDs

High‐performance, ink‐jet printable OLED materials have been successfully developed. Our wide libraries of platforms and small molecule hosts were effective for improving efficiency and lifetime of OLEDs. For wide color gamut, new emitters with deep in color and narrow full‐width at half maximum were developed. Further, solvent systems having physical properties suitable for improving film uniformity in pixels were found.

P‐106: Guest‐Host Liquid Crystal Devices Utilizing Dichroic Dye and Its Application

Wide application of dichroic dye‐doped liquid crystal device (DLCD) devices has been proposed, which removes conventional film‐type polarizer in reflective LCD and OLED. Combination of DLCD, quarter‐wave film and reflector can realize effective reflective LCD. In addition, by replacing conventional polarizer to switchable DLCD in OLED, the proper level of a low reflection is achieved, and more interestingly high brightness OLED can be realized if the optic axis of DLC is switched to vertical alignment when there is no ambient light, which could save power consumption and life time of OLED. Further DLCD can be applied to bi‐functional device functioning as both smart mirror and light shutter.

Influence of ambient temperature on OLED lifetime and uniformity based on modified equivalent lifetime detection

AbstractThe ambient temperature can affect the OLED heat dissipation and aggravate the luminance degradation. Based on temperature‐related equivalent lifetime detection, a luminance compensation algorithm without internal or external sensing circuits is proposed and the influence of ambient temperature on lifetime and display uniformity is studied. First, the parameters of luminance degradation curves at any ambient temperature are calculated according to the relationship between accelerate degradation factor n and ambient temperature T, which is determined by the measured luminance degradation curves at ambient temperature 25°C, 45°C, and 80°C. Second, luminance compensation is carried out by increasing drive current according to the estimated luminance degradation influenced by temperature. Furthermore, compensation iterations m, compensation goal value Lgoal, and compensation origin value Lorigin are optimized to obtain a better lifetime extension at different ambient temperature. The simulated and experimental results indicate that the lifetime extensions considering the influence of ambient temperature at 0°C, 25°C, 45°C, 60°C, and 80°C are 29.7%, 28.1%, 18.7%, 18.9%, and 11.6%. Meanwhile, after displaying an image of the International Electrotechnical Commission (IEC) 62087 for 90 hours, the luminance uniformity of OLED increase to 96.0%, 94.0%, 97.2%, 97.2%, and 98.6%, which is a significant improvement compared with it of regardless the influence of the ambient temperature.

White organic light emitting devices based on ultrathin emitting layer and bipolar hybrid interlayer

In this paper, efficient phosphorescent white organic light-emitting diodes (WOLEDs) with stable spectra are fabricated based on doping-free ultrathin emissive layers and mixed bipolar interlayers. To achieve WOLEDs, at least three kinds of light-emitting layers, i.e. blue, green and red, are needed. The traditional method to fabricate emissive layers is by co-evaporation, which can improve electroluminescent efficiency. However, the co-evaporation rate and dopant concentration are difficult to control, which leads to a bad reproducibility and thus goes against commercialization. In order to simplify the structures of WOLEDs and improve repeatability, several doping-free ultrathin emissive layers are used in this paper with 3 nm mixed bipolar interlayers separating them. The optimal ratio of bipolar hybrid material is determined by hole-only device, electron-only device and blue phosphorescent OLED. In addition, green, orange and red monochromatic OLED have also been fabricated separately, which are used to prove that mixed bipolar material is also suitable for the three phosphorescent emitting material. The WOLED with TCTA interlayers is fabricated to confirm that mixed bipolar material is beneficial to the characteristics of WOLEDs. The energy transfer process between different emitting materials is verified by studying the transient photoluminescence lifetime. The maximum efficiency of three-color and four-color doping-free WOLED are 52 cd/A (53.5 lm/W) and 13.8 cd/A (13.6 lm/W), respectively, and the maximum external quantum efficiency of three-color and four-color doping-free WOLED are 17.1% and 11.2%, respectively. Due to the sequential energy transfer structure between different emitting layers, the Commission Internationale de L'Eclairage coordinates shows a very slight variation of (0.005, 0.001) from 465 cd/m<sup>2</sup> to 15950 cd/m<sup>2</sup> for three-color WOLED. The Commission Internationale de L'Eclairage coordinates shows a variation of (0.023, 0.012) from 5077 cd/m<sup>2</sup> to 14390 cd/m<sup>2</sup> for four-color WOLED. The four-color WOLED shows a maximum color rendering index of 92.7 at 884 cd/m<sup>2</sup>, and it reaches 88.5 at 14390 cd/m<sup>2</sup>. In addition, the lifetime of phosphorescent OLED is usually poor due to the trap formed by triplet-polaron annihilation. The exciton distribution can be broadened and the exciton concentration can be reduced by using ultrathin light emitting layers (< 1 nm) and mixed bipolar interlayers. Therefore, triplet-polaron annihilation will be reduced, and the lifetime of OLEDs will be improved.

A Novel Voltage-Programmed Pixel Circuit with Poly-Si TFTs for AMOLED Displays

In this paper, we propose a novel voltage-programmed pixel circuit with polysilicon thin–flim transistors (poly-Si TFTs) for active matrix organic light-emitting diode (AMOLED) displays, which consists of one programming transistor, one driving transistor, four switching transistors and two storage capacitors, respectively. Specifically, the proposed pixel circuit is able to not only efficiently compensate for the threshold variations of TFTs, but also largely suppresses the electrical degradations of the devices caused by the long-term electrical stress. Moreover, the mobility variation of the driving transistor can be compensated as well. The simulation has been performed by HSPICE, and results indicate that the average values of nonuniformities are, respectively, 7.3% as the threshold-voltage varies by [Formula: see text][Formula: see text]V and 2.1%, as the mobility of the driving transistor varies by [Formula: see text]%, both of which are much lower than that of the conventional two-transistor and one-capacitor (2T1C) pixel. Furthermore, since the OLED is reverse-biased during the nonemission phases, the lifetime of OLED will be extended naturally. As a consequence, the proposed pixel circuit can substantially improve the display performance.

P‐207: Late‐News Poster: Efficient Emitter Aggregation Management Using High‐Entropy Non‐crystallizable Hosts

Molecular Glasses Inc. has developed a new class of high‐entropy non‐crystallizable OLED hosts that can be deposited by both vacuum/thermal evaporation and solution‐based processes such as inkjet printing. Benchmark testing demonstrated a 4‐15 times improvement in OLED lifetime using these hosts instead of conventional host 3, 3‐di(9H‐carbazol‐9‐yl) biphenyl (mCBP). Time resolved photoemission spectroscopy on a yellow phosphorescent emitter in a non‐crystallizable host – OLEDIQTM HT‐1700 vs. standard mCBP host shows that aggregation quenching is higher in mCBP. Triplet‐triplet annihilation (TTA) in these hosts is also explored.

19.2: OLED Lifetime Improvement Based on Optimization of Luminance Compensation Considering Luminance Uniformity

19.2: OLED Lifetime Improvement Based on Optimization of Luminance Compensation Considering Luminance Uniformity

Simultaneous Emission AC-OLED Pixel Circuit for Extended Lifetime of OLED Display

This paper demonstrates a pixel circuit of seven thin film transistors (TFTs) and two capacitors that drives an AC driven OLED (AC-OLED) at a simultaneous emission scheme. Because the AC-OLED is composed of two OLED units connected in opposite directions, the proposed circuit drives the current programmed once during a frame time in both ways. Since one OLED unit emits the light for about half frame time, the lifetime of OLEDs is ameliorated substantially. In addition, the proposed pixel circuit allows threshold voltage and supply voltage variations to be compensated. SPICE simulation results with a p-channel low temperature poly-silicon TFT model show that the average current non-uniformities are improved to 1.19% and 3.37% for threshold voltage and supply voltage variations of ±0.5 V, respectively.

3‐3: Influence of Vacuum Chamber Impurities on OLED Degradation

We evaluated the influence of impurities in the vacuum chamber used for device fabrication on the lifetime of OLEDs and found a correlation between lifetime and the device fabrication time. Our results suggest that impurities including previously deposited materials and plasticizers from the chamber components impact lifetime and reproducibility.

P.124: Ultra‐thin Flexible Encapsulation Layer for OLED Displays using Graphene Oxide Nanocomposite

AbstractUltra‐thin flexible nano‐composite encapsulation layer consists of graphene oxide and PDDA bi‐layer was prepared using layer‐by‐layer processing method. The encapsulation layer on PET substrate decreased WVTR of the substrate by more than three orders of magnitude and lifetime of OLED on the PET substrate was similar to that on glass substrate.

Al Top Cathode Deposition on OLED Using DC Magnetron Sputtering

AbstractWe fabricated OLEDs having the evaporated Yb cathode and the sputtered Al cathode. Magnetron sputtering is a versatile deposition method, but the energetic particles during sputtering process can damage the underlying organic layers. We applied various process parameters to explain the role of Ar neutrals quoting the former researches. OLEDs showed almost comparable degradation under the discharge voltage of 300 V, but serious degradations were found at the discharge voltage of over 300 V and the low process pressure. The degradations influenced on the lifetime of OLED, and the measured luminance decay was much larger than the OLED having the evaporated Yb cathode due to the high leakage currents.

P-202: Novel Electron Transporter and Hole Injector for OLEDs with Improved Device Characteristics and Longer Lifetime

The search for stable electron transporters and hole injectors has become particularly intense over the last 12 months as OLED manufacturers are poised to start production of OLED panels. We report here a proprietary electron transporter (E246), which reduces the operating voltage, increases the efficiency and the lifetime of OLEDs made of fluorescent or phosphorescent systems when compared with Alq3 as an electron transporter. We also report a novel proprietary hole injector (buffer, E9363) which also reduces the operating voltage, increases the efficiency and doubles the lifetime compared to CuPC. E246 has been validated on both ULVAC and Tokki vacuum evaporators. These two materials are now available commercially for display manufacturers.

A New AC-Driving Method for Active-Matrix OLED Displays

The lifetime of organic light-emitting devices can be influenced by the OLED material and structure, electrode material, driving mode and so on. Among all these factors, OLED driving method has been regarded as one of the most important factors, and it is well known that ac-driving mode improves the lifetime of OLED, especially pulse-driving mode with a reversed-biased voltage on OLED. In this article, a new ac-driving mode for Active-Matrix OLED is proposed on basic fabrication of two-TFT current source pixel circuit. Simulation has been done on the pixel and 1×4 matrix circuits, and simulation results have demonstrated that OLED is in reversed-biased state during recovery time. At last, a practical peripheral circuit that can provide achieve an ac-driving mode has been designed.

44.3: High-Aperture Ratio AMOLED Pixel Design Employing VDD Line Elimination for Reducing OLED Current Density

A new high-aperture ratio AMOLED pixel design scheme improving OLED life-time is proposed. The VDD supply line in each pixel is eliminated and the scan line supplies VDD to a pixel, thus a high-aperture ratio of emission area is considerably increased. The increased emission area achieves a lower current density through OLED, so that the OLED degradation would be suppressed and the life-time of OLED may be improved without varying the OLED materials. We also designed a storage capacitor employing the bank layer dielectric between ITO and cathode rather than typically used VDD line.

33.4: Thermal Treatment for the Longer Operating Lifetime of Organic Light Emitting Diodes

AbstractThermal effects on OLEDs display after full fabrication process including an encapsulation process have been studied for the longer operating lifetime of OLEDs. Time and temperature were considered as experimental factors to optimize thermal treatment. Brightness and voltage changes after thermal treatment at the optimized condition were negligible. However, the operating lifetime of OLEDs with proper thermal treatment was significantly improved.