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Lithium fluoride (LiF) is a widely used interlayer in organic optoelectronic devices, at both top and bottom electrodes, with various mechanisms proposed for its effectiveness at each interface. Here we examine the influence of LiF at the ITO electrode as a function of surface coverage. Both thermally evaporated LiF and LiF nanoparticles deposited from solution using di-block copolymer reverse micelles were used to probe the effect of island coverage on device characteristics. From hole-only devices (HOD) with a deep highest occupied molecular orbital (HOMO) level, capacitance–voltage and current–voltage characteristics show that LiF is effective only in the submonolayer range. Injection of holes is maximized at ∼ 12 % coverage, and decreases with increasing coverage of LiF. Above a critical surface coverage ( ∼ 50 % ), the barrier to injection becomes greater than that of bare ITO surface, but is mediated by dipole-induced interfacial trap states. Eventually, the barrier becomes so high that charge carriers cannot be effectively injected and the device does not operate. Using this insight, we fabricated blue phosphorescent organic light-emitting diode (PHOLED) using the optimal coverage of LiF nanoparticles, and observed maximum luminous and quantum efficiency that were improved by 30%. The effect of an array of LiF nanoparticles on emitter orientation was observed by angular-dependent photoluminescence spectroscopy. With this deeper understanding of how LiF operates at the ITO surface, it will be possible to further tune electrode interfaces to accommodate organic transport layers with deeper HOMO levels and larger bandgaps for next-generation devices. [ABSTRACT FROM AUTHOR]

Blue phosphorescence organic light-emitting diodes (PHOLEDs) with interfacial mixed layer (IML) were fabricated to observe their electrical characteristics. The IML was composed of mCP as host material in the emissive layer (EML) and 3TPYMB as material for the electron transport layer (ETL) with the blue phosphorescent dopant FIrpic. PHOLEDs with IML were improved by 41% of current density and 35% of luminous efficiency compared to PHOLEDs without IML. The electron and energy transition mechanisms between EML and ETL in the presence of IML were confirmed through I-V-L characteristics and blue color coordinates. [ABSTRACT FROM AUTHOR]

Green phosphorescent top-emitting organic light-emitting diodes (TOLEDs) based on a single ultrathin non-doped emissive layer (EML) are investigated for utilizing the cavity standing wave effect to enhance device performance. Furthermore, double ultrathin non-doped EMLs separated by a bi-layer structure is introduced to balance charges and further improve the efficiency. [ABSTRACT FROM AUTHOR]

We fabricated white phosphorescent organic light-emitting diodes (PHOLEDs) with the primary color(Red, Green and Blue) in single emissive layer using NPB, TCTA and TAPC as hole transporting layer (HTL) having different triplet energy level to observe triplet exciton's behavior. White PHOLED with TAPC having higher triplet energy level shows 51cd/A of luminous efficiency, and CIEXY color coordinate of (0.35, 0.40) at 10V. [ABSTRACT FROM AUTHOR]

To achieve the emissive layers in white organic light-emitting diode (WOLED) for the three primary colors, DCJTB doped in Alq3, C545T doped in Alq3, and BCzVBi doped in MADN were applied for red, green, and blue emissive layer, respectively. By stacking all the red, green, and blue emissive layers in a single device, WOLED devices with the color coordinates close to (0.33, 0.33) were successfully fabricated. The structure of the blue–green–red (BGR) type of the three primary color WOLED device was NPB(700 Å)/MADN:BCzVBi-13%(210 Å)/Alq3:C545T-2%(30 Å)/Alq3:DCJTB-2%(60 Å)/Alq3(300 Å)/Liq(20 Å)/Al(1000 Å). Its maximum luminance and luminous efficiency were 25,680 cd m−2 and 3.79 cd A−1, as well as its white color coordinate was (0.32, 0.31) at 7 V. The structure of blue–red–green (BRG) type of the three primary color WOLED device was NPB(700 Å)/MADN:BCzVB-13%(210 Å)/Alq3:DCJTB-2%(30 Å)/Alq3: C545T-2%(60 Å)/Alq3(300 Å)/Liq(20 Å)/Al(1000 Å). Its maximum luminance and luminous efficiency were 26,010 cd m−2 and 4.95 cd A−1, as well as its white color coordinate was (0.33, 0.33) at 7 V. Both devices were successfully induced closer to the ideal white emissive lighting source, and three different peaks at 480 nm, 512 nm, and 616 nm could be confirmed at red, green, and blue region in electroluminescence (EL) spectra. [ABSTRACT FROM AUTHOR]

We fabricated high contrast red, green, blue organic light-emitting diodes using inorganic metal multi layer (IMML) composed of thin Al, KBr, and thick Al. High contrast OLEDs using IMML were observed to compare with conventional OLEDs with circular polarizer and bare metal-electrode normal OLEDs. Average ambient reflectance of OLEDs using inorganic multi layer, polarizer OLEDs, and normal OLEDs were 18.2, 31.1, and 82.5% respectively. Contrast ratio of inorganic metal multi-layer OLED with red emission and polarizer attached OLED were same as 186:1 especially. [ABSTRACT FROM AUTHOR]

We investigated the effects of molecular ordering on the electro-optical characteristics of organic light-emitting diodes (OLEDs) with an emission layer (EML) of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV). The EML was fabricated by a solution process which can make molecules ordered. The performance of the OLED devices with the molecular ordering method was compared to that obtained through fabrication by a conventional spin coating method. The turn-on voltage and the luminance of the conventional OLEDs were 5 V and 34.75 cd/m2, whereas those of the proposed OLEDs were 4.5 V and 120.3 cd/m2, respectively. The underlying mechanism of the higher efficiency with ordered molecules was observed by analyzing the properties of the EML layer using AFM, SE, XRD, and an LCR meter. We confirmed that the electrical properties of the organic thin film can be improved by controlling the molecular ordering of the EML, which plays an important role in the electrical characteristics of the OLED. [ABSTRACT FROM AUTHOR]

Abstract: We have developed an image reversal photoresist with high thermal stability and electric insulating properties for small molecule organic light-emitting diode (SMOLED) applications. The thermal stability and electric insulating properties were investigated and compared to those of the conventional insulation layer and cathode separator materials of SMOLEDs. Moreover, to verify its applicability and reliability, 1.17″ 96×RGB (red, green, and blue subpixels)×96 passive matrix SMOLEDs were fabricated using the image reversal photoresist. This image reversal photoresist makes a single isolation structure, where the insulation layer and cathode separators of SMOLEDs are simultaneously formed by a single layer of image reversal photoresist, applicable to SMOLEDs, thereby reducing the fabrication processes and cutting down the manufacturing cost. [Copyright &y& Elsevier]

We used various emissive layer (EML) structures with ultrathin red EMLs to enhance the charge carrier balance and carrier recombination rate in blue PHOLED devices. These EML materials have different energy gaps between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels. The ultrathin red EMLs, which were inserted in between the blue EMLs, effectively confined the charge carriers in EML, and increased the carrier recombination rate. The thickness of the individual EML was optimized, under 30 nm of the total thickness of EML. The blue PHOLEDs with ultrathin red EMLs achieved a luminous efficiency of 19.24 cd/A, which was 28.7% higher than those without ultrathin red EMLs, and the maximum external quantum efficiency was 11.81% at 500 cd/m 2 . [ABSTRACT FROM AUTHOR]

Blue phosphorescent organic light-emitting diodes (OLED) using mixed electron transport layer (ETL) were fabricated with the device structure of ITO/NPB/mCP:Firpic-8%/TPBi:BCP or TPBi:3TPYMB/Liq/Al to observe mixed ETL’s influence on their electrical and optical characteristics. OLED device with mixed ETL of TPBi with BCP or 3TPYMB significantly improved its current efficiency to 30.4 and 34.2 cd/A comparing to 19.8 cd/A of single ETL with BCP only. We examined mixed ETL’s capability of electron transport and triplet exciton confinement enhancing phosphorescent OLED’s luminance and luminous efficiency. [ABSTRACT FROM AUTHOR]

Abstract: We demonstrate blue organic light-emitting diodes (OLEDs) based on a host-dopant system with a dual emitting layer (EML) configuration consisting of variable concentration of fluorescent doped and fixed concentration of phosphorescent doped emitting materials. We also introduce two different device designs by switching the position of the fluorescent and phosphorescent EMLs. Because 4,4'-Bis(2,2-diphenylvinyl)-1,1'-biphenyl (BCzVBi), which is the blue fluorescent dopant, exhibits the highest occupied molecular orbital (HOMO) energy level compared to the neighboring layers, the fluorescent dopant is shown to strongly correlate with hole transport in the fabricated blue OLEDs. In this study, we show how the electrical and optical properties of devices are affected by different doping concentrations due to the hole-transport-related properties of dopant molecules. [Copyright &y& Elsevier]

Abstract: For the high luminance and quantum efficiency, we propose a novel structure of white organic light-emitting diode (WOLED) using two white emissive layers (EML). The host material of MADN with the blue dopant of BCzVBi and the red dopant of DCJTB was used for one EML and DPVBi as host material with those dopants for the other EML. By considering the order of the EMLs and their energy band gaps in the device structure, the charge carrier trapping can be generated. They play a role in the barrier function at the EML enhancing the recombination where the holes and electrons were trapped in the DPVBi and MADN. The quantum efficiency can be improved by the charge carrier trapping in the WOLED with the double white EMLs as obtaining 4.23% at 10mA/cm2, and it is vastly superior to that of the WOLED with a single EML. White color balance is also excellent with color coordinates of (0.36, 0.34) in the CIE 1931 (x, y) chromaticity diagram. [Copyright &y& Elsevier]

Abstract: Green organic light-emitting diode (OLED) was fabricated using metal–inorganic–metal multi layer composed of thin Al, KCl and thick Al for achieving high contrast without polarizer. The ambient light reflection of OLED using inorganic metal multi layer, polarizer and conventional metal layer are 28.8, 26.9, and 82.1%, respectively. However, OLED with inorganic metal multi layer has high luminescence of 7367cd/m2, luminous efficiency of 1.81cd/A at 8V, and power efficiency of 0.91lm/W at 5.5V whereas OLED with polarizer has 6919cd/m2, 1.03cd/A at 8V, and 0.56lm/W at 5.5V each. The optical interference effect of inorganic metal multi layer showed possibility of replacing current polarizer to obtain higher contrast ratio in OLED. [Copyright &y& Elsevier]

2.4-in. organic light emitting diode panel with blue monochrome emission and resolution of 160×160 has been fabricated by using vacuum evaporation. It has the device structure of ITO/CuPc/NPD/DPVBi/Alq3/LiF/Al:Li(0.1 wt%) as of anode/hole injection layer/hole transport layer/emitting layer/electron transport layer/hole blocking layer/cathode respectively, and total thickness of organic layers besides anode and cathode electrode is 131 nm. Conventional photolithographic process was applied for patterning ITO, insulator and cathode separator and open aperture ratio of each pixel is 64.4%. Driving module selected the PWM method to embody the color depth of 16 gradations with the electric current control and it introduced a dual scan method that considered the panel brightness increase and device stability. [Copyright &y& Elsevier]