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In this study, a white light organic light-emitting diode is fabricated by solution processes. The focus of the research is to extend the lifetime of device. A hole transport layer doped with P-type material (F4-TCNQ) and a stepped electron transport layer TPBi (blocking holes and lowering the LUMO energy level) were employed in the device structure. And each layer thickness was optimized. At 9 V, the brightness can reach 206 cd/m2, current efficiency 1.29 cd/A, and the device lifetime is extended from 0.8 to 8 hours. The CIE color-coordinates of white OLED samples are (0.38, 0.28).

Most small molecule organic light emitting diode (SM-OLED) device structures are made in one layer using solution-based processing because the solution is usually a high dissolvent material that easily attacks the layer below it. We demonstrate a simple and reliable stamping technique for fabricating multi-solution process flexible white SM-OLEDs. The structure is anode/spin-hole injection layer/spin-emitting layer/stamping-electron transport layer/cathode. Poly(di-methyl silane) (PDMS) stamp is used for transferring electron transport layer. An intermediate ultraviolet-ozone surface treatment is introduced to temporarily modify the PDMS stamp surface. Then, the solution-based electron transport layer film can therefore be uniformly formed on top of the PDMS surface. After that the electron transport layer film on the PDMS stamp is transfer-printed onto the emitting layer with suitable heating and pressing. A solution-based processing is successfully established to efficiently fabricate flexible white SM-OLEDs. The SM-OLEDs were obtained at the current density of 20 mA/cm 2 , luminance of 1062 cd/m 2 , current efficiency of 5.57 cd/A, and Commission internationale de l'eclairage coordinate of (0.32, 0.35).

In this paper, the flexible white organic light-emitting diodes (WOLED) was fabricated on polyethylene naphthalate (PEN) with structure of ITO/EHI608 (75 nm)/HTG-1 (10 nm)/3% EB502:0.8% EY53 (5 nm)/3% EB502 (35 nm)/Alq3 (10 nm)/LiF (0.8 nm)/Al (150 nm) and was compared with glass substrate the same structure. It was seen that the performances of flexible and glass substrate are almost the same. The luminance, current efficiency, and CIE coordinates of flexible device is 6351 cd/m2, 12.7 cd/A, and (0.31, 0.38) at 50 mA/cm2, respectively. Then, an Al2O3/HfO2 film on polyethylene terephthalate (PET) was deposited using atomic layer deposition (ALD) as a thin film encapsulation layer have been described and compared, such as the characteristics of water permeability and lifetime of flexible WOLED. The results show that the PET/ALD film low value of about 0.04 g/m2d, and the PET film shows WVTR of about 3.8 g/m2/d. The lifetimes of PET/ALD and PET encapsulations are 840 min and 140 min, respectively. Simultaneous deposition of ALD film on PET film gave the lifetime of flexible WOLED is six times longer than device without ALD encapsulation.

Display Omitted Investigating PhOLEDs with different solvents and dopants concentrations.High efficiency white PhOLEDs induced by the electron transport/hole blocking material.To achieve efficient and low-cost small-molecule-based white PhOLEDs. In this study, white phosphorescent organic light-emitting diodes (PhOLEDs) have been demonstrated with small molecule by using solution processes. Spin-coating is employed as the way for deposition method. 4,4'-N,N'-dicarbazole-biphenyl (CBP) which is typical small molecule based ink is used for spin-coating method, and three phosphorescent dopants materials, Firidium(III) bis(4,6-difluoro phenyl)-pyridinato-N,C2'] picolinate (FIrpic), bis1-(phenyl) isoquinoline) iridium(III) acetyl acetonate (Ir(piq)2 (acac))], and iridium(III) tris(2-phenylpy-ridine) (Ir(ppy)3) were prepared. For spin-coating processes, various parameters properties were investigated including materials concentrations, solvents effect, and electron transporting materials to get high efficiency and white color of white PhOLED device. As a result, the precisely controlled solution processes could be a promising technology for solution process can be a good alternative of vacuum deposition technology.

In this research, complex emitting layers (EML) were fabricated using TCTA doping hole-transport material in the front half of a bipolar 26DCzPPy as well as PPT doping electron-transport material in the back half of 26DCzPPy. Blue dopant FIrpic was also mixed inside the complex emitting layer to produce a highly efficient blue phosphorescent organic light emitting diode (OLED). The hole and electron injection and carrier recombination rate were effectively increased. The fabricated complex emitting layers exhibited current efficiency of 42 cd/A and power efficiency of 30 lm/W when the luminance was 1000 cd/m 2 , driving voltage was 4.4 V, and current density was 2.4 mA/cm 2 . A white OLED component was then manufactured by doping red dopant [Os(bpftz) 2 (PPh 2 Me) 2 ] (Os) in proper locations. When the Os dopant was doped in between the complex emitting layers, excitons were effectively confined within, increasing the recombination rate and therefore reducing the color shift. The resulting Commission Internationale de L’Eclairage (CIE) coordinates shifted from 4 to 10 V is (Δ x =−0.04, Δ y =+0.01). The component had a current efficiency of 35.7 cd/A, a power efficiency of 24 lm/W, driving voltage of 4.6 V and a CIE x , y of (0.31,0.35) at a luminance of 1000 cd/m 2 , with a maximum luminance of 15,600 cd/m 2 at 10 V. Attaching an outcoupling enhancement film was applied to increase the luminance efficiency to 30 lm/W.

Hybrid white organic light emitting diodes (HWOLEDs) with fluorescence and phosphorescence hybrid structures are studied in this work. HWOLEDs were fabricated with blue/red emitting layers: fluorescent host material doped with sky blue material, and bipolar phosphorescent host emitting material doped with red dopant material. An electron blocking layer is applied that provides hole red guest emitter hole trapping effects, increases the charge carrier injection quantity into the emitting layers and controls the recombination zone (RZ) that helps balance the device color. Spacer layers were also inserted to expand the RZ, increase efficiency and reduce energy quenching along with roll-off effects. The resulting high efficiency warm white OLED device has the lower highest occupied molecule orbital level red guest material, current efficiency of 15.9 cd/A at current density of 20 mA/cm2, and Commission Internationale de L'Eclairage coordinates of (0.34, 0.39).

A mixed host emitting layer consisting of TCTA and 3TPYMB can greatly increase the efficiency of blue and white organic light emitting diodes (OLED). The hole transport material TCTA can be used as a buffer layer and a hole-transport host emitting layer. Combining TCTA with electron-transport 3TPYMB produces a mixed host emitting layer that can effectively confine the charge carrier within luminous layer. The electron transport layer 3TPYMB reduces electronic injection energy barriers, improves charge balance, and reduces drive voltage to 4.38 V with proper adjustment to optimum thickness. The luminous efficiency of blue light OLED mixed with FIrpic can reach 36.0 cd/A, 27.5 lm/W, and luminous efficiency of white light OLED mixed with Os tangerine adulterant can reach 36.1 cd/A, 26.4 lm/W.

A hybrid approach integrating a Taguchi orthogonal table with an irregular design of experiments (DOE) method was proposed for selecting an optimal material structure of blue organic light emitting diodes in order to achieve multi-objective quality characteristics of devices. Analysis of variance (ANOVA) was adopted to identify significant factors before regression models were obtained. Finally, an optimal material structure was determined by maximizing a desirability function relating to selected critical quality characteristics including the driving voltage, the luminance, and luminance efficiency.

White phosphorescent organic light-emitting diodes (WPHOLED) with high efficiency and low driving voltage were achieved by incorporating an electron transport material (3TPYMB) into a hole transport-type host (TCTA) as a mixed-host structure. For electrons, the emitting layer is nearly barrier-free until they reach the region of exciton formation, which keeps the driving voltage low. Therefore, improved the charge carrier balance within the emitting layer and enhanced the power efficiency of device. White PHOLED at a luminance of 1000 cd/m2 shown a driving voltage of 4.38 V, luminance efficiency of 36.1 cd/A, and power efficiency of 26.4 lm/W was observed. Furthermore, the power efficiency can be improved to 34.27 lm/W, and luminance efficiency to 46.7 cd/A by attaching a brightness enhancement film (BEF).

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.

We report an intuitive approach to simulating the performance of the phosphor-based light emitting diode (LED) by using the two-light-sources model for an optimized LED lens. The optimized secondary lens shape is achieved by approaching a uniform energy distribution on the detecting plane. Both the spectrum and spatial apodization of the LED structure are discussed, and the results indicate that the two-light-sources model can solve the misleading design on the phosphor-based LED due to imperfect color mixing of light source, that one can satisfy the highly uniformity requirement for specific applications, such as display backlight or optogenetic.

A blue small-molecular organic light-emitting diode (SM-OLEDs) based on a solution-process is investigated in this study. Design of experiment (DOE) with response surface methodology (RSM) was applied to optimize the driving voltage and current efficiency of blue SM-OLED devices. The spin-coating speed of the PEDOT: PSS as hole injection layer and the 26DCzPPy: FIrpic as emitting layer were chosen as two main process input factors. Analysis of variance (ANOVA) was adopted to identify significant factors before regression models were obtained. The optimal material structure was determined by minimizing and maximizing a desirability function relating to selected critical quality characteristics including the driving voltage and current efficiency, respectively.

In this research, the optimization of device structures of blue fluorescent organic light emitting diode (OLED) with WBH-301 doped with WBD-701 was fabricated. By adjusting the thickness of each layer in OLED structure as well as total thickness of device, the position of recombination zone was controlled and located in the central region of emitting layer (EML) that significantly increases device efficiency. The device showed the current efficiency of 8.7 cd/A at current density 50 mA/cm2 and with Commission Internationale de L’Eclairage (CIE) coordinates (x = 0.17, y = 0.34). This efficiency enhancement is important for understanding and further improving high-performance fluorescent OLEDs.

The use of numerical simulation method to study the current–voltage (I–V) of organic light emitting diode (OLED) has always been an effective method to upgrade the luminous efficiency of OLED. As the I–V theoretical simulation equations are based on injected carrier passing through Schottky barrier, and considering that carrier capturing defect and carrier mobility rate might be generated within the inner organic layer of Pool–Frenkel model, the study had made a comparison between the I–V theoretical model with a double-layer device and the experimental data, and proposed the best parameters for the theoretical model after careful adjustment and comparison to establish an optimal simulated numerical model with a double-layer OLED current–voltage. Finally, a study was made on the carrier capturing defect and mobility rate affected by electric field and temperature.

Solution-based processing was applied to fabricate green phosphorescent organic light-emitting diodes (OLEDs). EPH31 was used as a phosphorescent host, doped with guest dopant green phosphorescent Ir(ppy)3, and dissolved in chlorobenzene solvent to form the emitting layer. Device structural parameters were controlled by changing the spin coating speed of the emitting layer and hole injection layer [poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate), PDOT:PSS] to adjust the thickness of the electron transport layer [tris(8-hydroxyquinolinato)aluminum, Alq3]. In addition, the differences in using CsF and LiF materials as the electron injection layer were investigated. A maximum current efficiency of 13.6 cd·A-1 was obtained at a high emitting layer spin coating speed. Despite the close resemblance in both the luminance intensity and current efficiency when using CsF and LiF as the electron injection layer, CsF devices had a low driving voltage. Smooth and stable films resulting from the spin coated hole injection layer, along with the control of the thickness of the electron transport layer (Alq3) and electron injection layer (CsF), effectively improved the performance of green OLEDs. The emitting layer host material (CBP) and three guest dopants [Firpic, Ir(ppy)3, and Ir(piq)2] were dissolved in toluene solvent during solution preparation to fabricate white OLEDs. The properties of the resulting solution-processed white PHOLEDs are a current efficiency of 2.4 cd·A-1 at 20 mA·cm-2 and CIE coordinates of (0.33, 0.33) at 9 V. Results of these experiments demonstrate that solution processing can be used as an alternative to and in conjunction with thermal evaporation.

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.