Rationale Organic light‐emitting diode (OLED) products based on display applications have become popular in the past 10 years, and new products are being commercialized with rapid frequency. Despite the many advantages of OLEDs, these devices still have a problem concerning lifetime. To gain an understanding of the degradation process, the authors have investigated the molecular information for deteriorated OLED devices using time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS). Methods TOF‐SIMS depth profiling is an indispensable method for evaluating OLED devices. However, the depth profiles of OLEDs are generally difficult due to the mass interference among organic compounds, including degradation products. In this study, the tandem mass spectrometry (MS/MS) depth profiling method was used to characterize OLED devices. Results After degradation, defects comprised of small hydrocarbons were observed. Within the defect area, the diffusion of all OLED compounds was also observed. It is supposed that the source of the small hydrocarbons derives from decomposition of the OLED compounds and/or contaminants at the ITO interface. Conclusions The true compound distributions have been determined using MS/MS depth profiling methods. The results suggest that luminance decay is mainly due to the decomposition and diffusion of OLED compounds, and that OLED decomposition may be accelerated by adventitious hydrocarbons present at the ITO surface.
OLEDs, the manufacturing process and production yields should be improved to reduce the overall cost.The structure of an OLED device consists of an organic thin film layered between two electrodes (anode and cathode), and is a self-emitting device that emits light when holes and electrons injected from the electrodes recombine in the light-emitting layer upon application of a DC voltage. [1] A transparent anode (e.g., indium-tin-oxide (ITO)) is formed on a glass or other substrate, on which a hole injection layer (HIL), hole transport layer (HTL), emission layer (EML), electron transport layer (ETL), electron injection layer (EIL), and cathode (e.g., aluminum (Al)) are stacked. An organic layer is fabricated by a vacuum process such as vacuum deposition [2] or a solution process using spin-coating, slot-die coating, and ink-jet printing. [3][4][5][6] Each organic layer is very thin, with a total thickness of ≈100-200 nm. However, in contrast to the film thickness, it has a large emitting area of ≈10 × 10 cm 2 , especially for lighting applications. Owing to the low thickness of the device, even a small amount of microscale dust particles on such a large substrate causes defects, such as electrical short circuits and lower production yields of OLED panels. [7,8] Therefore, to solve this problem in OLED panel manufacturing, a system that strictly controls the microscale particles throughout the manufacturing process is needed.Although dust-induced short-circuit defects are a significant issue in the production of OLED panels, there are few reports on the mechanism. Based on the existing literature on the shortcircuit defects reported, we classified the factors of shortcircuit defects in OLED panels and their prevention methods by their fabrication process (Table 1). Several phenomena can cause short-circuit defects in the series of processes used for the fabrication of OLEDs. First, in the anodic sputtering process on a clean substrate, the flake particles generated from the sputtering target cause short-circuit defects. It has been reported that these factors can be prevented by smoothing the spattering anode (R peak-to-valley (R pv ) < 20 nm). [9][10][11] Moreover, in the electrode patterning process (photolithography), the steep step of the electrode edge, the resist residue after development, and resist mist on the substrate in photolithography are factors that can cause short-circuit defects. To prevent these problems, the formation of edge covers using insulators [12,13] and optimization of the photolithography process [14] have been reported.Short-circuit defects caused by microscale dust particles in organic lightemitting diodes (OLEDs) cause a decrease in production yield and hinder cost reduction. An organic layer coating by solution process is used to prevent short-circuit defects of particles on a substrate. In this study, the coverage properties of a coated organic layer on size-controlled particles are revealed. The surface of the substrate with size-controlled SiO 2 particles with a diameter of 0.2-5...
Wet-processable and low temperature curable hole injection polymer was demonstrated. It has good solubility to aromatic solvents and its thin film after the curing with initiator showed enough solvent resistance. It was confirmed to have the potential as Hole Injection Layer (HIL) by applying to blue fluorescenceOLEDs. Author Keywords hole injection polymer; wet-processable; low temperature curable; flexible organic light emitting diodes P-167 / K.-i. Ishitsuka SID 2018 DIGEST • 1789 ISSN 0097-996X/18/4703-1789-$1.00
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