Enhanced Hole Injection Characteristics of a Top Emission Organic Light-Emitting Diode with Pure Aluminum Anode

A top emitting organic light-emitting diode (OLED) device with pure aluminum (Al) anode for high-resolution microdisplays was proposed and fabricated. The low work function of the Al anode, even with a native oxide formed on the Al anode surface, increases the energy barrier of the interface between the anode and hole injection layer, and has poor hole-injection properties, which causes the low efficiency of the device. To enhance the hole-injection characteristics of the Al anode, we applied hexaazatriphenylene hexacarbonitrile (HATCN) as the hole-injection layer material. The proposed OLED device with a pure Al anode and native oxide on the anode surface improved efficiency by up to 35 cd/A at 1000 nit, which is 78% of the level of normal OLEDs with indium tin oxide (ITO) anode.

Light Extraction Efficiency Analysis of Phosphorescent OLED Device with Microlens Array on the Glass Substrate

The Computational simulation is based on the desired packing type of microlens array, either hexagonal or rectangular, onto the planar dual scheme OLED device's light-emitting surface. Both active layers here acted as a phosphorescent emission layer studied to improve device efficiency. The microlens array (MLAs) with hexagonal packing can increase the external quantum efficiency by 35%, which is more than the literature mentioned earlier. It significantly enhances the outcoupling efficiency below the critical angle observation concerning the substrate surface normal. Besides, a broad spectrum is observed with a slight shoulder band around 650 nm in the E.L. (Electroluminance) emission curve. From the CIE x and CIE y index studied, the OLED device connected with either hexagonal or rectangular microlens arrays are more sensitive than the OLED device without microlens arrays to the viewing angle range. The effect of outcoupled efficiency as a function of ETL-TPBi thickness is studied under different polarization modes. Hence, the study suggested that a microlens array with a hexagonal or rectangular packing type on the OLED device's top significantly enhanced light extraction efficiency and provided better device fabrication results.

Design Simulation and Preparation of White OLED Microdisplay Based on Microcavity Structure Optimization

White-light OLED devices play an important application in information display fields. Optical interference of the microcavity structure has an important effect on device performances. According to the design of the band structure, ITO/MoO3 composite films were used as the anode, and Mg : Ag (1%) composite films were prepared by coevaporation as the translucent cathode; CuPc was used as the hole injection layer and anode passivation layer, NPB as the hole transmission layer and yellow light main material, rubrene as yellow dopant material, ADN as blue light main material, DSA-Ph as blue dopant material, and TPBi and Alq3 as the electron transport layers. We realized the change of the microcavity structure by adjusting the thickness of each organic functional layer film and simulated and calculated the optimized thickness of each organic film layer and influence on OLED device performances using the SimOLED software system. The optimized OLED microdisplay structure is Si(CMOS)/ITO (35 nm)/MoO3 (2 nm)/CuPc (5 nm)/2-TNATA (20 nm)/NPB (10 nm)/NPB : rubrene (1.5%)ADN : DSA-Ph (5%) (25 nm)/TPBi (15 nm)/Alq3 (1.2 nm)/Mg (13 nm) : Ag (1%). The optimized OLED microdisplay was prepared by the vacuum coating system, and the photoelectric performances of the OLED device were characterized by a spectral testing system consisting of the Photo Research PR655 spectrometer and Keithley 2400 program-controlled power supply. The effect of the microcavity structure on OLED device performances was studied. The results show that the variation of the film thickness of each organic functional layer has an important effect on the performances of OLED microdisplay, such as brightness and color coordinate, and the OLED microdisplay reaches a higher brightness of 3342 cd/m2 under the normal working voltage at 5.0 V after the structure is optimized, with CIE coordinate (0.28, 0.37), which is closer to the energy point of standard white light.

Protecting benzylic C–H bonds by deuteration doubles the operational lifetime of deep blue Ir-phenylimidazole dopants in phosphorescent OLEDs

Much effort has been dedicated to increase the operational lifetime of blue phosphorescent materials in organic light-emitting diodes (OLEDs), but the reported device lifetimes are still too short for the industrial applications. An attractive method for increasing the lifetime of a given emitter without making any chemical change is exploiting the kinetic isotope effect, where key C–H bonds are deuterated. A computer model identified that the most vulnerable molecular site in an Ir-phenylimidazole dopant is the benzylic C–H bond and predicted that deuteration may lower the deactivation pathway involving C–H/D cleavage notably. Experiments showed that the device lifetime (T70) of a prototype phosphorescent OLED device could be doubled to 355 hours with a maximum external quantum efficiency of 25.1% at 1000 cd/m2. This is one of the best operational performances of blue phosphorescent OLEDs observed to date in a single stacked cell.