A carbazole-based diaza[7]helicene, 2,12-dihexyl-2,12-diaza[7]helicene (1), was synthesized by a photochemical synthesis and its use as a deep-blue dopant emitter in an organic light-emitting diode (OLED) was examined. Compound 1 exhibited good solubility and excellent thermal stability with a high decomposition temperature (T(d)=372.1 °C) and a high glass-transition temperature (T(g), up to 203.0 °C). Single-crystal structural analysis of the crystalline clathrate (1)(2)⋅cyclohexane along with a theoretical investigation revealed a non-planar-fused structure of compound 1, which prevented the close-packing of molecules in the solid state and kept the molecule in a good amorphous state, which allowed the optimization of the properties of the OLED. A device with a structure of ITO/NPB (50 nm)/CBP:5 % 1 (30 nm)/BCP (20 nm)/Mg:Ag (100 nm)/Ag (50 nm) showed saturated blue light with Commission Internationale de L'Eclairage (CIE) coordinates of (0.15, 0.10); the maximum luminance efficiency and brightness were 0.22 cd A(-1) (0.09 Lm W(-1)) and 2365 cd m(-2), respectively. This new class of helicenes, based on carbazole frameworks, not only opens new possibilities for utilizing helicene derivatives in deep-blue-emitting OLEDs but may also have potential applications in many other fields, such as molecular recognition and organic nonlinear optical materials.
The electrical characteristics of the BCE-structure IGZO TFTs were studied. Through modifying the passivation layer and optimizing the selection of copper acid and PFA material, the TFTs exhibited good threshold voltage and reliability. Finally, a high performance 31-inch 8K4K GOA LCD was demonstrated.
In this paper, high reliable a-IGZO TFT gate driving circuit was designed. Series-connected two-transistor (STT) structure and dual low-voltage-level power signal (Vss) were used to solve the initial negative Vth of IGZO TFTs. Special pull-down holding part was designed for wider Vth shift window during panel operation. The Vth shift margin of this proposed GOA design is from -5V to +9V by using Eldo-Spice simulation system. In addition, the pullup control part could also play a role to pull the Q node voltage down and it is helpful for narrow border design. Finally, a 31-in. 8K4K 287-ppi TFT-LCD was successfully demonstrated based on the study above.
Illumination instability of BCE IGZO TFT was studied in this paper. It was found that the distance between island‐in IGZO and gate electrode is larger than 2μm (P2) could be able to resist light induced device deterioration effectively. We also found that P4 was an optimum distance for flicker performance compared to P2 design, the flicker level of P2 and P4 is 25dB and HdB respectively. Finally, a high performance 32‐inch 8K4K IGZO LCD was successfully demonstrated based on all the study above.
A 31-inch FHD (1920x1080) AM-OLED TV was developed by using a-IGZO TFTs. Co-planar type of a-IGZO TFT was fabricated at Gen 4.5 glass substrate with IGZO (1:1:1
) AC sputtering system for AM-OLED. We also used Fine Metal Mask (FMM) for R,G,B sub-pixel arrangement.
Two different a‐IGZO gate driving circuits (GOA) which used long channel length (GOA_A) and STT (GOA_B) structures were designed and compared. GOA_B shows better performance than that of GOA_A, while the Vth of T53 in GOA_B circuit would shift to a very positive voltage after life test. The large channel width size ratio between T53 and T54 would bring about bigger Vds voltage of T53 which induces large current stress of T53 in GOA_B, so the Vth voltage of T53 in GOA_B would shift to a very positive voltage at life test. The phenomenon which T53 devices were easy to shift to positive bias can be restrained and improved by new design of its pull down holding part in GOA_B by spice simulated results.
Top-emitting active-matrix organic light-emitting diode (AMOLED) displays usually use a thin cathode layer to obtain high transmittance. However, the thin surface cathode inevitably raises an IR drop issue or even a Mura effect that is visible to the naked eyes, especially in large-size displays. Therefore, to reduce the IR-drop effect and improve the display quality, a plurality of cathode separators are provided to separate the cathode of AMOLEDs to electrically connect the cathode to the auxiliary electrodes under the cathode separators. In this work, we report how to control the process of organic photoresist to obtain a good anti-taper (cathode separator). The organic photoresist is formed through the steps of coating, pre-bake, exposure, post exposure bake (PEB) and then developing, but the exposure and PEB processes are the key factors, which can improve the anti-taper below 53° (The EL evaporation angle is 53°).
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