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The effect of the phosphor doping concentration on the optoelectronic characteristics of white phosphorescence organic light emitting diodes (PHOLEDs) was studied. A high efficiency white PHOLED was achieved using the unique efficiency properties of the red-emitting Osmium complex ([fptz = 3-trifluoromethyl-5-(2-pyridyl)-1,2,4-triazole, PPh2Me = phosphineligand]; Os(fptz)2(PPh2Me)2) combined with a well known efficient blue-emitting Iridium complex (bis[(4,6-difluorophenyl)-pyridinate-N,C2′; FIrpic]). The results demonstrate that with 2 wt% Os(fptz)2(PPh2Me)2 co-doped into the blue-emitting layer (10 wt% FIrpic doped into the host), the device can achieve a luminance efficiency of up to 40.4 cd/A (25.6 lm/W) with a good corresponding CIE coordinate (0.39, 0.40). The doping concentrations of the red-emitting and blue-emitting phosphors were adjusted to obtain a pure white light with a CIE coordinate of (0.368, 0.366). A high efficiency white PHOLED was achieved by optimizing the doping concentration of the red-emitting and blue-emitting complexes.

The characteristics of blue phosphorescent organic light-emitting diodes (PHOLEDs) with hole–buffer structure were investigated by inserting a hole transport-type host (TCTA) between the hole transport layer (HTL, TAPC) and emitting layer (EML, FIrpic:26DCzPPy). The hole transport-type host has lower hole mobility than the HTL material, which could effectively control the hole injection current from the HTL into the EML. Moreover, the hole injection barrier from HTL to EML can be reduced due to the suitable HOMO level of the insertion hole buffer layer, which results in the improvement of driving voltage. Furthermore, the power efficiency was improved by controlling the hole injection current through buffer layer thickness optimization. From the experimental results, an optimal blue PHOLED structure was established: ITO/TAPC(20 nm)/TCTA(25 nm)/FIrpic:26DCzPPy(20 nm)/3TPYMB(40 nm)/LiF(0.5 nm)/Al(200 nm). At luminance of 1000 cd/m2, the driving voltage decreased from 6.3 to 5.1 V and power efficiency enhanced from 6.7 to 13.5 lm/W could be observed.

UV-curable organic/inorganic hybrid composites with gas barrier and heat-dissipating capability have been successfully fast synthesized with microwave irradiation and utilized for the encapsulation of top-emitting organic light-emitting diodes (TEOLEDs). Experimental results manifest that lab-made organic/inorganic hybrid composites can effectively not only obstruct the invasion of moisture as well as oxygen in the atmosphere into the device but also lower the temperature of device. Therefore, the lifetimes of TEOLEDs with their encapsulation are 2.2 folds longer than those without encapsulation.

A high heat dissipation material (copper, Cu) was employed as the substrate for top emission organic light-emitting diodes (TEOLEDs). The UV glue was spin-coated onto the Cu substrate as the insulation layer to effectively improve Cu surface roughness and reduce process complexity. From the optoelectronic results, the optimized device with the Cu substrate shows the maximum luminance of 14110 cd/m2 and luminance efficiency of 7.14 cd/A. The surface and junction temperatures are measured to discuss the heat-dissipating effect on device performance. From the results, TEOLED fabricated on a Cu substrate has lower junction (55.34°C) and surface (25.7°C) temperatures, with the lifetime extended seven times. We employed Cu foil as the substrate for flexible TEOLED with maximum luminance of 10310 cd/m2 and luminance efficiency of 7.3 cd/A obtained.

In this article, we report on the effect of SiO 2 /Si 3 N 4 dielectric distributed Bragg reflectors (DDBRs) for Alq 3 /NPB thin-film resonant cavity organic light emitting diode (RCOLED) in increasing the light output intensity and reducing the linewidth of spontaneous emission spectrum. The optimum DDBR number is found as 3 pairs. The device performance will be bad by further increasing or decreasing the number of DDBR. As compared to the conventional Alq 3 /NPB thin-film organic light emitting diode (OLED), the Alq 3 /NPB thin-film RCOLED with 3-pair DDBRs has the superior electrical and optical characteristics including a forward voltage of 6 V, a current efficiency of 3.4 cd/A, a luminance of 2715 cd/m 2 under the injection current density of 1000 A/m 2 , and a full width at half maximum (FWHM) of 12 nm for emission spectrum over the 5–9 V bias range. These results represent that the Alq 3 /NPB thin-film OLED with DDBRs shows a potential as the light source for plastic optical fiber (POF) communication system.

We dissolved hole transport materials α-NPD and NPB in THF solvent, and spin-coated the α-NPD + THF or NPB + THF solution onto ITO anode surface to improve the luminance efficiency and lifetime of flexible fluorescent and phosphorescent organic light emitting diodes. Then the BCP and TPBi were employed as hole blocking layer (HBL) of phosphorescent device and its thickness was optimized. From the experimental results, the maximum luminance efficiency is 4.4 cd/A at 9 V of fluorescent device and 24.4 cd/A of phosphorescent device, respectively. Such an improvement in the device performance was attributed to the smoother surface and good contact between the interface of spin-coated HTL/ITO, the hole were effectively injected from the anode into the organic layer. And the deposited HTL can block excitons from diffusing into the anode to quench, thus improving the luminance efficiency and lifetime greatly.

The triple-metal-layer periodic structures in the anode for top-emission organic light-emitting diodes (TEOLEDs) are reported in this paper. The anode consists of aluminum (Al) and nickel/gold (Ni/Au) periodic structures. The Al is used for high reflectivity and Ni/Au for high work function by enhancing the hole injection from the anode into the organic hole injection layer. The Ni and Au work functions were measured at 5.3 and 5.1 eV, respectively, which were higher than that of a single Al layer at 4.2 eV. This two pair Ni/Au anode device exhibits high reflectivity and reveals the microcavity effect to increase luminescence efficiency. The optimum current efficiency with the two pair Ni/Au anode is increased to 7.99 cd/A compared with the one pair Ni/Au anode (6.85 cd/A) and three pair Ni/Au anode (5.07 cd/A).

This work demonstrates the use of lithium fluoride (LiF) as a passivation layer and a newly developed UV glue for encapsulation on the LiF passivation layer to enhance the stability of organic light-emitting devices (OLEDs). Devices with double protective layers showed a 25-fold increase in operational lifetime compared to those without any packaging layers. LiF has a low melting point and insulating characteristics and it can be adapted as both a protective layer and pre-encapsulation film. The newly developed UV glue has a fast curing time of only 6 s and can be directly spin-coated onto the surface of the LiF passivation layer. The LiF thin film plus spin-coated UV glue is a simple packaging method that reduces the fabrication costs of OLEDs.

In this study, we employed an ultrathin separately doped organic light-emitting diode (OLED) structure to achieve the lowest turn-on voltage, highest luminance efficiency, and highest electroluminescence. In the simulation part, the spectrum intensity of the main emitting layer (EML) tris(8-hydroxy-quinoline) aluminum (Alq3) photoluminescence (PL) and the full width at half maximum (FWHM) of its Gaussian distribution were modulated to obtain the luminescence spectrum of an ultrathin separately doped device. It is found that as doping concentration increases, the extent of intensity modulation in simulation must be decreased in order to simulate the Alq3 peak drop. This result confirms that when the concentration of a red dopant is high, the red luminance is purer, but the brightness is weaker than that at a lower doping concentration; conversely, at a higher intensity a lower concentration of a red dopant results in more intense luminance, but an orange light, instead of a pure red light is emitted. This study aims to clarify how Alq3 intensity changes in, correspondence to different doping concentrations. For simulation results to coincide with the experimental data, it is deduced that the PL spectrum of 4-(dicuanomethylene)-2-methyl-6-(1,1,7,7-tetramethyljulol-idyl-9-enyl)-4H-pyran, DCJT (red dye), exhibits a red shift as doping concentration increases. Finally, we also adjust the thickness of organic layers (hole transport layer/EML) to more accurately approximate simulation results with respect to experimental data.

The organic light emitting diodes (OLEDs) [1] is a new-generation flat panel display with the advantages of self-luminescence, wide viewing angle (> 160°), prompt response time (~1 μs), low operating voltage (3~10 V), high luminance efficiency, high color purity, and easy to be made on various substrates. Therefore, it’s an important topic that how to improve the luminance efficiency, lifetime and the adhesion characters of ITO/organic interface of flexible OLEDs. Zugang Liu et al. reported that the NPB (HTL) is suitable in contact with the emission layer and when they form an energy ladder structure, the driving voltage decreased and the electroluminescent output increased [2]. Thus it can be seen, the hole transport layer [3-6] is very important to balance the injection of hole and electron, to increase the luminance efficiency and lifetime. In recent years, the hole buffer layer of device typically employs LiF [7], CuPc [8], Pani:PSS [9-10] or PEDOT:PSS [9-11] to improve the hole injection efficiency. In addition, a flexible substrate (PET, metal foil, etc.) surface is not completely smooth and will usually have spikes. After the organic thin film evaporates onto the ITO substrate surface the spikes will still exist. When the device is operated under high voltage or high current density, a heavy amount of electric current will concentrate at the spikes and damage the device by causing the device to short circuit, creating Joule heat. The luminance efficiency of the device will therefore be reduced producing shorter device lifetime. Thus, the PEDOT:PSS fabrication process uses spin-coating to obtain a thin film with a smoother surface than that produced by thermal deposition. Spin-coating enhances the organic material adhesion in subsequent processes, thereby directly affecting the performance of flexible OLED. For the above reason, this research dissolved hole transport material N,N’-diphenyl-N,N’-bis(1-naphthyl)1,1’biphenyl-4,4’’diamine (α-NPD), N,N’Bis(naphthalenel-yl) -N,N’-bis(phenyl)-benzidine (NPB) or α-NPD:NPB in tetrahydrfuran (THF) solvent and spin-coated the buffer layer onto ITO surface of flexible OLEDs. Phosphorescent dye gains energy from the radiative recombination of both singlet and triplet excitons [12], improving the internal quantum efficiency of fluorescent OLEDs (FOLEDs) typically 25% at maximum to nearly 100% [13]. Enhancing the luminance 8

In this study, we dissolved hole transport layer (HTL) material NPB in THF (tetrahydrofuran) solvant, and spin-coated the N,N'-Bis(naphthalene-l-yl)-N,N'-bis(phenyl)-benzidine (NPB) solution on the surface of Indium Tin Oxide (ITO) anode to enhance the luminance efficiency and lifetime of flexible phosphorescent organic light emitting diodes (POLEDs), where the 2,2',2''-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) was employed as hole blocking layer (HBL) and its thickness was optimized. Such an improvement in the device performance was attributed to the improved hole-electron balance. Finally, we employed 2,9-Dime-thyl-4,7-dphenyl-1,10-phenanhroline (BCP) or TPBi as hole blocking layer. The maximum luminance efficiency reaching 24.4 cd/A can be obtained.

This study is carried out to discuss how to reduce the driving voltage of blue phosphorescent organic light-emitting diodes (PHOLEDs) by using a thin double-emission layer. A hole transport-type host (TCTA) is inserted between the hole transport layer (TAPC) and the emitting layer (EML), constituting a buffer layer between them with the aim of improving charge carrier balance. Furthermore, in this study, we also utilize the interface between double light-emitting layers of devices by codoping them with a red phosphorescent dopant [Os(bpftz)2(PPh2Me)2]. An Os complex with a high-lying highest occupied molecular orbital (HOMO) energy level (trapping holes) is codoped at the interface between emitting layers and an exciton-formation zone is expanded to obtain a white PHOLED with high efficiency. From the results, the optimal structure of the white device exhibits a yield of 35 cd A-1, a power efficiency of 22 lm W-1, and CIE coordinates of (0.33,0.38) at a luminance of 1000 cd m-2. Furthermore, the power efficiency can be improved to 30 lm W-1 by attaching the outcoupling enhancement film.

The influence of heat dissipation on the performances of organic light-emitting diode (OLED) is investigated by measuring junction temperature and by calculating the rate of heat flow. The calculated rate of heat flow reveals that the key factors include the thermal conductivity, the substrate thickness, and the UV glue. Moreover, the use of copper substrate can effectively dissipate the joule heat, which then reduces the temperature gradient. Finally, it is shown that the use of a high thermal conductivity thinner substrate can enhance the thermal conductivity of OLED and the luminance efficiency as well.

In this study N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)-benzidine (NPB) was dissolved in tetrahydrofuran (THF) solvent, and the resulting solution was spin-coated onto an indium tin oxide (ITO)-coated plastic substrate to form the first hole transport layer (HTL). A second hole transport layer of NPB was then deposited by thermal evaporation on the first HTL to produce a flexible organic light-emitting diode (OLED) with a double HTL structure. The luminance efficiency of a device with a double HTL structure is thereby improved. Utilizing spin-coated (NPB+THF)/evaporated NPB as the double HTL structure, the efficiency can reach 3.86 cd/A, and the lifetime is extended by 14.4% compared with that of the conventional single thermally evaporated HTL.