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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.

In this study, we investigated the optimum thicknesses of organic light-emitting diode (OLED) layers using a high-reflectivity metal, Al, coupled with high-work-function alloys, e.g., AuSn, AuGe, and AuGeNi, as anodes, and LiF/Al/Ag multilayers as cathodes. The work function of a double-metal-layer, Al/AuGeNi (60/2 nm), was measured to be 4.7 eV, which is higher than that of a single Al layer of 4.2 eV. A high-work-function anode increased the number of holes injected from the anode into a hole transport layer and hence increased luminescence efficiency. After the optimization of each organic layer thickness, the device produced a maximum luminance of 2930 cd/m2 and a maximum luminance yield of 1.4 cd/A, which are the significant improvements of the performance characteristics of 537 cd/m2 and 0.28 cd/A obtained before the optimization of organic thickness, when the single Al layer was used as an anode, the device only exhibited a luminescence of 190 cd/m2 and a short lifetime.

This study employed poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate) (PEDOT:PSS), 4,4'-bis[N-(1-naphthyl)-N-phenylamino]-biphenyl (α-NPD) and α-NPD/Teflon as buffer layers between the organic layer and indium tin oxide (ITO) of a flexible organic light-emitting diode (FOLED) to enhance the luminance efficiency of the device. PEDOT:PSS and α-NPD were spin-coated onto the ITO substrate, but α-NPD was first dissolved in chloroform. With the deposition of PEDOT:PSS of 40 nm thickness, the surface roughness of ITO decreased from 2.768 to 1.415 nm, whereas the luminance yield increased from 2.0 to 4.0 cd/A; the maximum luminance was 1500 cd/m2 at 44 mA/cm2. With the deposition of α-NPD of optimum thickness as buffer layer, the device had a luminance yield of 5.2 cd/A and a maximum luminance of 1220 cd/m2 at 25 mA/cm2. When the α-NPD buffer layer was further coated with a thin layer of Teflon by evaporation, i.e., α-NPD/Teflon (55/1 nm), the luminance yield of the device increased to 6.5 cd/A.

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.

The derivatives of C60, [6,6]-phenyl C61-butyric acid methyl ester (PCBM), and 3-hexylthiophene (P3HT) were dissolved in o-dichlorobenzene (DCB) solvent, and then spin-coated as an active layer for polymer solar cells. The experimental parameters including the spin-coating speed and drying conditions for the active layer, were studied carefully to obtain the optimum power conversion efficiency (PCE). In the active layer drying procedure, the DCB solvent saturated/unsaturated vapor pressure was adjusted by controlling the amount of solvent at a half-open capacity. The DCB solution was used to enhance the self-organization of the active layer of P3HT and to reduce the number of pure PCBM clusters. In the DCB optimum solution, the PCE of a polymer solar cell can be increased from 1.36 to 1.79%. The structure corresponds to a nano-to-micron scale ordering in the unsaturation-treatment films. In the optimum unsaturation procedure, the PCE of a polymer solar cell can be increased from 1.79 to 2.53%. Using two steps with optimum rotation speeds in the active layer spin-coating, the surface uniformity can be improved, with the PCE increased from 2.53 to 3.13%.

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.

Polymeric solar cells (PSCs) with a derivative of C60 [[6,6]-phenyl C61-butyric acid methyl ester (PCBM)], and 3-hexylthiophene (P3HT) as active layers have been fabricated. The PSC devices were also packaged with glass and novel UV glues to improve their lifetimes and power conversion efficiencies (PCEs). After encapsulation with UV glue I, II, and III, the PCEs of PSCs reached 4, 4.82, and 6%, respectively, and their half-lifetimes increased to 16–18, 26–28, and 90 h, respectively, while the PCEs and half-lifetimes of PSCs without encapsulation were 3.76% and 2.5 h, respectively.

This paper reports on the separately-doped structures of organic light-emitting diodes (OLED) in which red dye 4-(dicyanomethylene)-2-methyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJT) was doped into the host emitting layer of tris(8-hydroxyquinoline)aluminum (Alq3) by means of ultrathin separate doping (like quantum wells). The parameters in the ultrathin layer, including its width, position, number and spacing between separately doped layers, were changed to study their effects on electroluminescence (EL) characteristics. Thin doped layers increase the luminance efficiency. When the ultrathin separately doped layers were in the vicinity of the NPB/Alq3 interface, where N,N'-diphenyl-N,N'-bis(1-naphthyl)-(1,1'-biphenyl)-4,4'-diamine (NPB) is used as a hole transport layer, luminance efficiency also increased. The highest luminance efficiency reaching 4 cd/A was achieved using a double ultrathin separately doped structure with optimum doping thickness and 2 nm of space between the two layers. The study also found that double ultrathin separately doped structures achieved better EL intensity than single or triple ultrathin separately doped structures.