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We carried out Monte Carlo simulation and clarified the variation in electron energy in layered optimized electroluminescent ZnS with high electric field. We found that the following: (1) 8 eV is necessary for the energy of primary electrons entering the luminescent layer with an electric field of 4 MV/cm in order to enhance the excitation of luminescence. (2) The distributions of both the density of states and the hot electron energy concentrate and shift to the high energy end when the electric field increases; thus most of the hot electrons are effective in the excitation of luminescence. (3) The average energy of hot electrons is found to reach a second plateau in a stepwise manner along the increase in electric field corresponding to the second jump in electroluminescence in a layered optimization scheme. [ABSTRACT FROM AUTHOR]

To inhibit concentration quenching, three new bis-tridentate iridium complexes modified with triptycene groups were successfully synthesized. The rigid sterically demanding triptycene endows these new complexes with high photoluminescence quantum yields (PLQYs) and low concentration quenching. In air, their PLQYs exceed 0.68 in poly(methyl methacrylate) (PMMA) films and 0.17 in neat powder form, which are significantly higher than that of the reference complex (0.57 and 0.03, respectively). At the same time, the thermal stability of the complex Ir1 is improved and the luminescence wavelength of the complex Ir1 is less affected by the modification of triptycene group. The doped OLED device based on complex Ir1 exhibits excellent electroluminescent efficiencies of 80.1 cd A−1 and 24.0%, which are improved by more than 50% compared with that of reference device. More significantly, the maximum efficiencies of its non-doped device are 17.6 cd A−1, 7.4%, which are improved by more than 300% compared with that of reference device. These results indicate that the triptycene group is very effective functional group to inhibit the concentration quenching of bis-tridentate iridium complexes. Complex Ir1 exhibited the PLQY of 0.73, T d of 379 °C and peak EQE 24.0% with mild roll-off. [Display omitted] • Three bis-tridentate Ir complexes with triptycene groups were synthesized. • All complexes are concentration-insensitive with high PLQYs. • Their PLQYs (0.18–0.35) in neat powder are significantly higher than contrast (0.03). • Best device exhibited high efficiencies of 80.1 cd A−1 and 24.0% with mild roll-off. • The efficiencies (doped/non-doped devices) are improved than contrast (>50%/300%). [ABSTRACT FROM AUTHOR]

While perovskite light-emitting diodes typically made with high work function anodes and low work function cathodes have recently gained intense interests. Perovskite light-emitting devices with two high work function electrodes with interesting features are demonstrated here. Firstly, electroluminescence can be easily obtained from both forward and reverse biases. Secondly, the results of impedance spectroscopy indicate that the ionic conductivity in the iodide perovskite (CH3NH3PbI3) is large with a value of ≈10−8 S cm−1. Thirdly, the shift of the emission spectrum in the mixed halide perovskite (CH3NH3PbI3−xBrx) light-emitting devices indicates that I− ions are mobile in the perovskites. Fourthly, this work shows that the accumulated ions at the interfaces result in a large capacitance (≈100 μF cm−2). The above results conclusively prove that the organic–inorganic halide perovskites are solid electrolytes with mixed ionic and electronic conductivity and the light-emitting device is a light-emitting electrochemical cell. The work also suggests that the organic–inorganic halide perovskites are potential energy-storage materials, which may be applicable in the field of solid-state supercapacitors and batteries. [ABSTRACT FROM AUTHOR]

We studied the luminescent and photovoltaic properties of poly(9,9-dioctylfluorene-co-bithiophene) (F8T2) based on ITO/PEDOT:PSS/F8T2/Bphen/LiF(0 or 1 nm)/Al and ITO/PEDOT:PSS/F8T2:PCBM/Bphen/Al. A stable and bright yellow emission was obtained from polymer F8T2, and the electroluminescence power reached 45 μW at a 15 V driving voltage. Polymer F8T2 shows a broad absorption band from 400 to 500 nm, and has a shorter absorption edge at about 560 nm compared to that of the typical electron donor P3HT (650 nm). The photoluminescence quenching of F8T2 occurs with only a small fraction of blended PCBM due to the effective exciton dissociation at the interface between F8T2 and PCBM. Polymer solar cells (PSCs) using F8T2:PCBM as the active layer show a low power conversion efficiency (PCE) of 0.10% with an open circuit voltage ( V) of 0.91 V and short circuit current density ( J) of 0.23 mA/cm. The PSCs using F8T2:P3HT:PCBM as the active layer have a V of 0.85 V and J of 3.02 mA/cm, improving the PCE by about 0.90%. We attribute the improved cell performance to the higher number of photons harvested by P3HT molecules. [ABSTRACT FROM AUTHOR]

Abstract: Wide band gap semiconductor zinc sulfide (ZnS) nanocolumn arrays were prepared on the glass side of ITO substrates by glancing angle deposition (GLAD) technology. The SEM images show the formation of ZnS nanocolumn arrays when the glancing angle was set to 80°; however, continuous ZnS thin films were fabricated under normal deposition (0°). The XRD spectra of the films show that the most intensive diffraction peak changed from (220) to (111) when the incidence angle was set to 0° and 80°. The transmitting ability of ITO substrate coated with ZnS nanocolumn arrays was enhanced compared with continuous ZnS thin films coated ITO substrate and bare ITO substrate in the visible range. Organic light emitting diodes (OLEDs) were simultaneously fabricated on these three kinds of substrates. The electroluminescence (EL) intensity of OLEDs based on the ITO substrate coated with ZnS nanocolumn arrays was about 1.3 times bigger than that of devices based on the other substrates (continuous ZnS film coated ITO substrates and bare ITO substrates) under the same driving voltage. [Copyright &y& Elsevier]

Abstract: Three kinds of organic light emitting diodes with tris(8-hydroxyquinoline) aluminum (Alq3) as emitting layers were fabricated. It was found that the current efficiency (8.2cd/A) of devices with pentacene as hole transporting layer (HTL) was obtained at 10V, which was increased by a factor of 3.2 in comparison with that (2.6cd/A) of the devices with N,N′-bis-(1-naphthyl)-N,N′-1-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) as HTL. The improvement was attributed to the large hole mobility of pentacene and the increased interfacial surface area induced by its pyramid-like morphology, which result in the increase of the recombination region at the interfaces between pentacene and Alq3 layers. Investigation by atomic force microscopy (AFM) shows the surface morphology of pentacene and NPB thin films. [Copyright &y& Elsevier]

Abstract: There is an emission peak at 494nm in the electroluminescence (EL) of PVK [poly(n-vinylcarbazole)]: Eu(o-BBA)3(phen) besides PVK exciton emission and Eu3+ characteristic emissions. Both the peaking at 494nm emission and PVK emission influenced the color purity of red emission from Eu(o-BBA)3(phen). In order to restrain these emissions and obtain high intensity red emission, 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7,-tetramethyljulolidy-9-enyl)-4Hpyran (DCJTB) and Eu(o-BBA)3(phen) were co-doped in PVK solution and used as the active emission layer. The EL intensity of co-doped devices reached to 420cd/m2 at 20V driving voltage. The chromaticity coordinates of EL was invariable (x =0.55, y =0.36) with the increase of driving voltage. For further improvement of EL intensity, organic–inorganic hybrid devices (ITO/active emission layer/ZnS/Al) were fabricated. The EL intensity was increased by a factor of 2.5 [(420cd/m2)/(168cd/m2)] when the Eu complex was doped with an efficient dye DCJTB, and by a factor of ≈4 [(650cd/m2)/(168cd/m2)] when in addition ZnS layer was deposited on such an emitting layer prior to evaporation of the Al cathode. [Copyright &y& Elsevier]

Abstract: The electroluminescence (EL) of lanthanide complex profits from the intramolecular energy transfer from the triplet state of ligand to Ln (III) ions, but electroplex emission between ligand and host material may occur when the energy transfer is inefficient. The electroplex emission is completely restrained when 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7,-tetramethyljulolidy-9-enyl)-4Hpyran (DCJTB) and Eu(o-BBA)3(phen) are co-doped in poly (N-vinycarbzaole) (PVK). There are great spectra overlapping between electroplex emission and the excitation of DCJTB. The chromaticity coordinates of EL of co-doped device is kept constant (x =0.55, y =0.37) under different driving voltage. [Copyright &y& Elsevier]

Abstract: A new organic–inorganic heterostructure device was designed. The wide gap semiconductor ZnS was acted as an electron transporting, electron acceleration and hole blocking layer. The combined structure of organic/inorganic device has three distinguished advantages: (i) avoid these uncontrolled phenomena on organic material interfaces; (ii) increase the energy and number of injected electrons into ploy (N-vinyl-carbazole) PVK (iii) enhance hole-current density by the increase of the electric field strength in PVK due to a high dielectric constant material ZnS as an electron transporting layer. Characteristic emissions of complex of terbium ion with o-benzoylbenzoate ion and 1, 10-phenathroline (Tb(o-BBA)3(phen)) based on organic–inorganic heterostructure device were obtained. The maximum EL intensity was improved more than three times and reached to 326cdm−2 compared with the pure organic electroluminescence device. [Copyright &y& Elsevier]

Abstract: An organic–inorganic heterostructure device was designed to improve the electroluminescence intensity of terbium ion. In this heterostructure, a mixed solution of (Tb(o-BBA)3(phen)) and poly(N-vinylcarbazole) (PVK) was prepared with a weight ratio of 3:1 which was acted as a hole transporting and emitting layer. A wide band semiconductor zinc sulfide (ZnS) layer was used as an electron transporting and hole blocking layer. Characteristic emissions of terbium ion from the organic–inorganic heterostructure device were observed and the electroluminescence intensity of terbium ion increased abruptly when the driving voltage went beyond 20.5V. This may be due to a directly impact excitation of terbium ion by hot electrons, accelerated in ZnS layer, and then a recombination with the injected holes. The electroluminescence mechanism of Tb(o-BBA)3(phen)-doped PVK was the charge-carrier trapping process by the dopant molecule according to the emission spectra of PVK and the excitation spectra of Tb(o-BBA)3(phen). [Copyright &y& Elsevier]

In organic electroluminescence there is a sharp contradiction between the applicability of band model and molecular theory. This contradiction arose from the very beginning of extended study. In this report we studied the blue spectral shift in the newly discovered solid state cathodoluminescence when the applied voltage is increased. There are three different kinds of spectra in three intervals of applied voltage. The reason of this spectral shift is found to be the field ionization of exciton. The switching on of recombination starts only after the beginning of this field ionization. The exciton emission obeys molecular theory and the recombination obeys band model. Thus the demarcation is the appearance of field ionization of excitons. Since the ionization changes with electric field continuously, there is a region of coexistence of these two processes. [ABSTRACT FROM AUTHOR]

Abstract: Influences of electric fields on the emission from organic light-emitting diodes (OLEDs) based on poly(N-vinylcarbazole) (PVK) and 4′-bis(2-2diphenylvinyl)-1,1′-biphenyl (DPVBi) as the active emission layer are studied. Electroluminescence (EL) spectra of PVK:DPVBi (1:1 w/w) films show one new emission peak locating at 640nm compared with its photoluminescence (PL) spectra. There may be exists an electroplex emission between the PVK and DPVBi under high electric field strength. The emission intensity of peaking at 640nm strongly depends on the driving voltage, and the ratio of electroplex emission intensity to exciton emission intensity (I electroplex/I exciton) increases with the increase of driving voltage. [Copyright &y& Elsevier]

Abstract: The authors report the fabrication of white organic light-emitting devices and discuss their electroluminescence (EL) properties. The device structure is ITO/TPD (50nm)/BCP (8nm)/Rubrene (0.5nm)/BCP (10nm)/Alq3 (20nm)/LiF (1nm)/Al. In the EL spectra of this device, two new emissions peaking at 590 and 630nm have been observed. These two emissions should be attributed to triplet exciplex and electroplex occurring at TPD/BCP interface. White emission was obtained based on this device under 12V driving voltage, the Commission Internationale de l’Eclairage (CIE) coordinates arrives to (0.31, 0.33). [Copyright &y& Elsevier]

Abstract: Organic light-emitting diodes (OLEDs) have been fabricated which consist of N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine) (TPD), 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), and tris(8-hydroxyquinoline) aluminum (Alq3). Four emission peaks located at about 401nm, 425nm, 452nm and 480nm have been obtained in the electroluminescence (EL) spectra of these devices. The former two emissions originate from the exciton emission of TPD molecular. The last two emissions could be attributed to local (LOC) exiplex emission and charge transfer (CT) exiplex emission at the interface between TPD and BCP layers, respectively. [Copyright &y& Elsevier]

Highlights: Two-dimensional poly[fluorene-alt-bithiophene] backboned copolymers with phenylvinyl bridged accepting side chain exhibit tuned bandgap and absorption spectrum with different accepting units, which may be used as promising electroluminescent materials. [Copyright &y& Elsevier]

[Display omitted] • Phase transformation was achieved via an insertion reaction with additive ZnBr 2. • Nonlumi nescent Cs 4 PbBr 6 were transformed to green Zn-doped CsPbBr 3 /Cs 4 PbBr 6 NCs. • The transformed Zn-doped CsPbBr 3 /Cs 4 PbBr 6 NCs exhibited high PL QY of 77.5%. • The transformed NCs based EL LED was fabricated with a record EQE of 3.2%. Zero-dimensional (0D) perovskites have attracted a great deal of attention over the last few years due to their fascinating properties. However, their application in electroluminescent (EL) Light-emitting diodes (LEDs) is limited and suffering from extremely low device performance. Herein, the nonluminescent Cs 4 PbBr 6 nanocrystals (NCs) were successfully transformed to highly luminescent Zn-doped CsPbBr 3 /Cs 4 PbBr 6 NCs via an insertion reaction with ZnBr 2 , which changed the atomic molar ratios of NCs and promoted the formation of CsPbBr 3. In this reaction, the Zn2+ ions provided by ZnBr 2 together with the Pb2+ ions can occupy the B-site due to the similar ion radius. The extra Br- ions not only can facilitate the transformation process, but also can passivate the surface defects of the NCs, resulting in high photoluminescence quantum yield (PL QY) of 77.5%. Furthermore, as-synthesized Zn-doped CsPbBr 3 /Cs 4 PbBr 6 NCs were used as emitters to fabricate EL LEDs. The device achieved the maximum current efficiency of 9.8 cd/A and a peak external quantum efficiency of 3.2%, which is the best performance of the CsPbBr 3 /Cs 4 PbBr 6 based LEDs. This reveals the great application potential of CsPbBr 3 /Cs 4 PbBr 6 NCs as EL emitters in LEDs. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, six organic light emitting devices with different quantum well cycles and different position of well structures have been demonstrated. These well structures were composed by N,N′-diphenyl-N,N′-bis(1-napthyl)-1,1′-biphenyl-4,4′-diamine and tris-(8-hydroxyquinoline) aluminum, or tris-(8-hydroxyquinoline) aluminum and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline. The device with one cycles well structure as electron transporting layer exhibits the highest brightness 3354cd/m2 and current efficiency of 3.46cd/A. The current efficiency improved owing to carrier confinement and higher exciton formation probability in the well layer. Results illustrated that using proper period of well structure could improve the current efficiency of organic light emitting device and using well structure as electron transporting layer are better than as hole-transporting layer. [Copyright &y& Elsevier]

Abstract: [6,6]-Phenyl C61 butyric acid methyl ester (PCBM) is used to modify an indium tin oxide (ITO)-coated substrate. Organic light-emitting diodes (OLEDs) using PCBM as the anode modification layer are fabricated. The dependence of performance on different PCBM thicknesses is also investigated. When the thickness of the PCBM film is appropriate, the brightness and efficiency of OLEDs are enhanced, which is attributed to an enhanced hole injection and an improved carrier balance. The enhancement of hole injection was ascribed to the formation of a dipole layer at the anode/organic interface. [Copyright &y& Elsevier]

Abstract: Rare earth complex Tb(PCAD)3Phen was synthesized by introducing 3-pyridylacetic acid (PCAD) and phenanthroline (1,10-Phen) as the ligands and characterized by UV, fluorescent, IR spectra and X-ray diffraction (XRD) as well as elemental analysis. The complex exhibited ligand-sensitized green emission, and it has higher sensitized luminescent efficiency and longer lifetime. In device ITO/PVK/Tb(PCAD)3Phen/Al, Tb3+ may be excited by intramolecular energy transfer from ligand as observed by electroluminescence. The main emitting peak at 545nm can be attributed to the transition of 5D4 → 7F5 of Tb3+ ion and this process results in the enhancement of green emission from electroluminescence device. The effect and mechanism of the ligands (PCAD and 1,10-Phen) on the luminescence properties of terbium complex were discussed. The present study may be important and helpful for the development of green color rare earth display applications. [Copyright &y& Elsevier]

Abstract: Three kinds of rare earth ternary complexes of Eu3+ with HTTA and M (M=5-NO2Phen, 2,2′-Dipy and TPPO) have been synthesized and characterized using various spectral techniques such as elemental analysis, TGA-DTA, IR, UV and fluorescent. Results show that the complexes of Eu(III) emit strong red luminescence when excited by UV light. The complex Eu(TTA)35NO2Phen posses the highest sensitized luminescent efficiency and the longest lifetime in the studied complexes. TG curves indicate that Eu(TTA)35NO2Phen is most stable. In device ITO/PVK/Eu(TTA)35NO2Phen/Al, Eu3+ may be excited by intramolecular energy transfer from ligands as observed by electroluminescence. The main emitting peak at 614nm can be attributed to the transition of 5D0 → 7F2 of Eu3+ ion, and this process results in the enhancement of red emission from electroluminescence device. [Copyright &y& Elsevier]

Abstract: Rare-earth ternary complexes Eu X Y1−X (TTA)3Dipy {X =0, 0.1, 0.25, 0.5, 0.75, 0.9, 1.0, using thenoyltrifluoroacetone (TTA) as ligand and 2,2′-dipyridyl (Dipy) as synergic agent} were synthesized. Characterization with X-ray diffraction (XRD), IR and elemental analysis had also been carried out. The photophysical properties of these complexes were studied in detail with ultraviolet absorption spectra and fluorescent spectra. It is found that the enhanced luminescence of Eu3+ ions by Y3+ ions occurs in ternary complexes. And we monitored the spectra of Eu X Y1−X (TTA)3Dipy (PVK:Eu/BCP/AlQ/Al) at the different rate (rpm). The results showed that the Y3+ ion acts as an energy transfer bridge that helps energy transfer from PVK to Eu3+. [Copyright &y& Elsevier]

Abstract: In this work, organic/inorganic heterostructure electroluminescence devices are fabricated, in which the inorganic layers (ZnO, ZnS) act as the electron transfer layer and the hole blocking layer. Compared to single-organic-layer (MEH-PPV) devices, the heterostructure devices have a significantly enhanced luminous efficiency. The influences of the electric field and the barrier potential on the improvements in performance are analyzed in detail. The results are: (i) the introduction of the inorganic layer makes the injection of electrons easier; (ii) the hole current density is enhanced by the increase of the electric field in the organic layer due to a high dielectric constant of the inorganic layer and accumulation of electrons at the inorganic/organic interface; (iii) the electron–hole current density balance is improved. [Copyright &y& Elsevier]

Abstract: A novel rare-earth complex of europium ion with 2-benzoylbenzoic acid and 1,10-phenathroline (Eu(o-BBA)3(phen), o-BBA=2-benzoylbenzoic acid, phen=1,10-phenathroline) was synthesized, and used as a luminescent material for the first time. The Eu complex was blended with poly(N-vinylcarbazole) (PVK) and spin coated into films (noted as PVK:Eu films). Monolayer devices with the structure ITO/PVK:Eu/Al were fabricated and they emitted red light, which was characteristic of Eu3+ emission. The results showed that the mechanism for photoluminescence (PL) and electroluminescent (EL) was different. The PL was considered to be caused because of energy transfer and direct excitation of Eu(o-BBA)3(phen), while EL was mainly due to charge trapping. [Copyright &y& Elsevier]