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High performance blue phosphorescent organic electroluminescent devices were realized by utilizing trivalent terbium complex and iridium complex as co-dopant and emitter, respectively. In this case, the co-doped trivalent terbium complex molecules within light-emitting layer function as deeper electron trappers due to its low-lying energy levels. Compared with reference device, co-doped devices displayed relatively higher electroluminescent performances due to improved carriers' balance as well as broadening recombination zone. Finally, the optimal device with main emission peak at 462 nm obtained the maximum brightness, external quantum efficiency, current efficiency and power efficiency up to 24396 cd/m2, 26.3%, 46.93 cd/A and 50.82 lm/W, respectively. Meanwhile, even at the practical brightness of 1000 cd/m2 (4.3 V), prominent external quantum efficiency and current efficiency as high as 24.0% and 40.73 cd/A, respectively, can still be retained because the broadening recombination zone helps to decrease exciton density thus suppress exciton quenching. [Display omitted] • High performance blue phosphorescent OLEDs were realized. • Trivalent terbium complex and iridium complex were utilized as co-dopant and emitter, respectively. • Co-doped trivalent terbium complex molecules within EML function as deeper electron trappers. • Co-doped devices displayed higher EL performances due to improved carriers' balance and broadening recombination zone. [ABSTRACT FROM AUTHOR]

• Raman and FTIR characterization of PTDPV vibrational modes and photoluminescence. • Comparison of experimental and DFT simulated Raman and IR spectra of PTDPV. • Use of Franck Condon method to rebuilt photoluminescence spectra at 300 K. • Identification of the vibrational frequencies (1117, 1288 and 1558 cm−1) that contribute to the PL vibronic bands. • Manufacture of electroluminescent devices, from the PFO:PTDPV (92%:08%) blend, with white emission. The polymer Poly[tris(2,5-bis(hexyloxy)-1,4-phenylenevinylene)-alt-(1,3-phenylenevinylene)] (PTDPV) has a broad range of visible emission extending from green to red, and thus may be useful for obtaining a white light emitting blend. Nevertheless, the amount of works found in the literature dealing with the optical emission properties of PTDPV is very small. In this work, we performed a study of the optical properties of this material using photoluminescence and of the vibrational properties using Raman and Fourier Transform Infrared Spectroscopy (FT-IR) techniques. At the same time, we use the Density Functional Theory (DFT) method to calculate the optical, vibrational and molecular properties of PTDPV. We have obtained the best DFT results using a hybrid functional and a simple basis set (DFT / B3LYP and 6–31 g *), without addition of correction or polarization factors (+). To reach these conclusions, we compared the HOMO and LUMO values obtained via DFT with those found in the literature. Furthermore, the Raman and IR simulations obtained using this basis set were compared with the experimental results of the PTDPV, showing great agreement. From the vibrational modes obtained, it was possible, using the Lin model [ 1–3 ], based on the Franck Condon approximations, to reconstruct the photoluminescence spectrum of the PTDPV. Based on these reconstructed spectra, it was possible to establish the contribution of the different vibrational modes to the vibronic emissions of the photoluminescence spectrum. The quality of the reconstruction obtained with the DFT results and that obtained with the experimental ones are very close, showing the possibility of using in this reconstruction the calculated vibrational modes when the experimental ones are not available. To demonstrate the application of this material, PFO:PTDPV blends were prepared, with which white photoluminescence was obtained. OLEDs prepared with these blends, in suitable proportions, emitted white light using low excitation power, demonstrating the feasibility of using PTDPV in OLEDs for lighting, which could be prepared by solution on large areas. [ABSTRACT FROM AUTHOR]

The electroluminescent (EL) properties of two polyfluorene-based (poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO) and poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)] (F8BT)) organic light-emitting diodes (OLEDs) were investigated. Two diode configurations were tested: blends with emissive layers of PFO (higher weight percentage, from 98 to 99.8 wt.%) and F8BT (lower weight percentage, from 0.2 to 2 wt.%) and bilayers of PFO/F8BT. To understand the diode performances, we compared the photoluminescence (PL) and the EL emissions of both configurations. PL emission decays showed that the fluorescence resonant energy transfer (FRET) efficiency is higher for blends that have less of the F8BT component than in bilayers. For the bilayer systems, however, the FRET efficiency is approximately 50%, confirming the significant inter-penetration of these two polymers. Upon decreasing the F8BT concentration in the blend or the F8BT film thickness in the bilayer, the EL emission shifted toward the blue color due to a more significant contribution from the PFO emission. The EL color can be tuned between green (from the F8BT) and blue (from the PFO) shades by adjusting the polymer composition. The differences between the PL and EL band profiles were discussed. [ABSTRACT FROM AUTHOR]

Two homoleptic iridium(III) complexes Ir3F and Ir6F were synthesized and tested as wide bandgap organometallic hosts for green phosphorescent OLEDs. While using Ir(ppy) 3 as the green triplet emitter, Ir3F -based devices clearly outperformed similar devices fabricated with the traditional CBP host. On the opposite, Ir6F -based devices showed lower performances than the reference device. As appealing feature, Ir6F -based devices showed almost no efficiency roll-off i.e., no reduction of the luminous efficiency with the current density contrarily to that commonly observed for phosphorescent OLEDs. [ABSTRACT FROM AUTHOR]

Two heteroleptic iridium complexes were synthesized and their photophysical properties studied. The two complexes vary by their ancillary ligand that is respectively acetylacetone (acac) or dibenzoylmethane (dbm). Interestingly, only the acac-based complex proved to be highly emissive and electroluminescent devices were only fabricated with this complex. In order to determine the emissive properties of this new complex, comparison with complexes previously reported in the literature was established. [ABSTRACT FROM AUTHOR]

Abstract: A novel white organic electroluminescent device was fabricated by inserting a thin lithium fluoride (LiF) layer in the emitting layer (tris-(8-hydroxyquinoline) aluminum (Alq3)). The electroluminescence device with the configuration indium tin oxide (ITO)/N,N′-diphenyl-N,N′-bis(l-napthyl)-1,1′-biphenyl-4,4′-diamine (NPB; 45nm)/tris-(8-hydroxyquinoline) aluminum (Alq3; x nm)/LiF (0.3nm)/Alq3 ((45− x)nm)/Al (150nm) showed expanded electroluminescence (EL) spectra. The spectra contain tricolor, so this should be a simple method to realize white light emitting. We also elucidated the mechanism of expanded EL spectra formation and investigated the properties of these devices. [Copyright &y& Elsevier]

Abstract: The results of an experimental study of the electroluminescent device made of ITO/CuI/2,6-di-tert.-butyl-4-(2,5-diphenyl-3,4-dihydro-2H-pyrazol-3-yl)-phenol (HPhP)/3,6-Di(9-carbazolyl)-9-(2-ethylhexyl) carbazole (TCz1)/Ca:Al with efficacy up to 10.63cd/A are presented. HPhP provides blue emission with a peak wavelength at 445nm. The layer of TCz1 acts as an electron-transporting layer. In the framework of density functional theory (DFT) approach the geometry configuration and energy levels of HPhP are found being in a good agreement with spectral and cyclic voltammogram data. [Copyright &y& Elsevier]

Abstract: By introducing a triarylamino and three-coordinate boron groups into a fluorene bridge, an asymmetric and bipolar compound, 2-dimesitylboron-7-(N-phenyl-α-naphthyl-amino)-9,9-diethylfluorene (BNPEF), was prepared. Light emissions of BNPEF were different in solvents of different polarities. A series of electroluminescent devices was fabricated. Device A ITO/BNPEF/LiF/Al, Device B ITO/NPB/BNPEF/LiF/Al, Devices C and D ITO/NPB/BNPEF/BCP/AlQ3/LiF/Al, Device E ITO/BNPEF/AlQ3/LiF/Al and Device F ITO/NPB/BNPEF/AlQ3/LiF/Al, were fabricated. Device A exhibited a blue emission at 456nm. Device B showed a green emission at 512nm with current efficiency of 0.67cd/A. The blue EL peaks of Devices C and D were at 488 and 484nm with current efficiencies of 2.92 and 5.03cd/A, respectively. Devices E and F emitted green lights at 520 and 528nm with current efficiencies of 4.03 and 2.35cd/A, respectively. The characteristics of the devices demonstrated that BNPEF was a multifunctional molecule acting as a blue emitting, or hole- or electron-transporting materials. [Copyright &y& Elsevier]

Abstract: Electroluminescent (EL) phenomenon has been widely used in the illumination industry such as light emitting diode (LED) and organic light emitting diode (OLED) nowadays. In this research, flexible EL devices were fabricated by using the flexible substrates and conductive polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) dispersions as the anode materials. The PEDOT:PSS dispersion was firstly prepared by oxidative polymerization while PSS was served as a polymeric template. Via introducing poly(vinyl pyrrolidone) (PVP) ethanol solution into the PEDOT:PSS dispersion, viscosity and wetting ability of the mixed PEDOT:PSS/PVP solution were enhanced in the same time. The three formed PEDOT:PSS/PVP thin films on glass substrates presented good conductivity and high transmittance (transmittance >76%). The wetting abilities of these PEDOT:PSS/PVP dispersions on the PET films coated with the low dielectric resin were evaluated from the contact angle measurements. It showed that the contact angle was decreased with increasing the addition of PVP ethanol solution. The different PEDOT:PSS/PVP dispersions were further used as the anode material in the EL flat plates and EL wires by dip coating process. Uniform and smooth conductive thin films with high transmittance were formed on the low dielectric resin layer. The luminance of these EL devices was observed and photographed after connecting to 110V AC power. [Copyright &y& Elsevier]

Abstract: This investigation discusses the performance of an organic light-emitting device (OLED) with ultraviolet (UV) illuminated and remote pulsed Ar plasma (RPAP), treated copper phthalcyanine (CuPc) thin film on an indium tin oxide anode as the hole-blocking layer. UV treatment increased the driving voltage, the current efficiency decreased at the same time due to the poor sticking probability of NPB on the CuPc surface. By contrast, the driving voltage reduction and current efficiency enhancement were achieved at the same time for the OLED with the RPAP treated CuPc. Besides this, in such device, the thickness of CuPc affects seldom the current density–voltage–luminance characteristics. The surface characteristics of these processed CuPc thin films were investigated by using atomic force microscope, contact angle and X-ray photoelectron spectroscopy measurements, which showed the CuPc/, N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) interface was crucial to not only the interface energy barrier, but also the following NPB growth, mode. [Copyright &y& Elsevier]

Abstract: A phosphorescent cyclometalated heteroleptic Ir(III) complex was investigated as emitter for light-emitting electrochemical cells (LECs) and polymer organic light-emitting diodes (POLEDs). By exploring the deposition conditions of the emissive layer in multilayered electroluminescent devices, we directly impacted the emission color by mixing or not the complex with poly(vinylcarbazole) (PVK). Strategy of emission color tuning enabled to produce blue or yellow emitting devices. Heteroleptic complex was characterized by UV–visible absorption and luminescence spectroscopy. Cyclic voltammetry and DFT calculations were also performed. [Copyright &y& Elsevier]

Abstract: The electroluminescent device ITO/CuI/3,6-di(9-carbazolyl)-9-(2-ethylhexyl)carbazole(TCz1)/Ca/Al in which TCz1 for the first time was used as the emitting layer, was fabricated by means of vacuum deposition. The device emits blue light with a peaks at 388 and 406nm at 4.5V, with high current efficiency values (11.5cd/A) and external quantum efficiency (1.72%). [Copyright &y& Elsevier]

Abstract: Tris-(8-hydroxyquinoline) metal complex Znq2, used as light-emitting layer in electroluminescent (EL) devices was synthesized and optical properties of as-deposited Znq2 in thin films were studied. Interesting phenomenon was observed while studying the ageing and degradation behavior of Znq2 films and consequently a stable form having strong blue photoluminescence (peak 465nm) was discovered. This converted (from green to blue emitting) film has higher molecular packing density and comparable photoluminescence intensity with Znq2 film. Here, we report on the production of this blue material under controlled conditions and its optical properties. The thin films have been deposited by thermal evaporation on quartz and silicon substrates. The optical constants (n and k) of green Znq2 film and converted (to blue) thin films have been determined using spectroscopic ellipsometry. Environment induced effects on optical properties of films have been studied using ellipsometry, photoluminescence and UV–vis transmission measurements. [Copyright &y& Elsevier]

Abstract: A new class of aryl amine derivatives, which contains phenylnaphthyldiamine core, has been synthesized and examined as a hole-transporting material (HTM) for organic light-emitting diodes (OLEDs). These phenylnaphthyldiamine derivatives possess high radical cation stabilities and high morphologic stabilities relative to their biphenyldiamine analogs. Theoretical experiments and OLED device fabrication were carried out to study their better hole-transporting properties. The electroluminescent devices with the phenylnaphthyldiamine derivatives HTM 2–4 as the hole-transporting layer were more efficient than that with the biphenyldiamine HTM 1. [Copyright &y& Elsevier]

Abstract: Color stable and interlayer free hybrid white organic light-emitting diodes were fabricated by using an area divided pixel structure. The area divided pixel structure was realized by stacking red and blue emitting layers using a fine metal mask. A phosphorescent red emitting layer was patterned by a metal mask and a blue fluorescent emitting layer was commonly deposited on the patterned red emitting layer. The blue fluorescent emitting layer could play a role of a hole-blocking layer and a white emission could be obtained due to separate emission of red and blue emitting layers. The interlayer free hybrid WOLEDs showed color stability from 100cd/m2 to 10,000cd/m2. [Copyright &y& Elsevier]

Abstract: New spiro-type 5-biphenyl-spiro[fluorene-7,9′-benzofluorene] (BH-1BP) and 5-diphenyl amine-spiro[fluorene-7,9′-benzofluorene] (BH-1DPA) were synthesized for use as blue organic light-emitting host and dopant materials, respectively. Their optical properties, including their UV absorption, photoluminescence and energy levels, were measured and blue OLEDs were made from them. The structure of the blue device is ITO/DNTPD/α-NPD/BH-1BP:5% dopant/Alq3 or ET4/Al–LiF. Here, α-NPD is used as the hole transport layer, DNTPD as the hole injection layer, BH-1DPA or diphenyl-[4-(2-[1,1;4,1]terphenyl-4-yl-vinyl)-phenyl]-amine (BD-1) as the blue dopant materials, Alq3 or ET4 as the transporting layer and Al as the cathode. The blue devices doped with 5% BH-1DPA and BD-1 show blue EL emissions at 444–448nm at 7V. A high efficiency of 3.28cd/A and the CIE coordinates (0.14, 0.11) at 7V can be achieved from the devices composed of BH-1BP:5% BD-1/ET4. [Copyright &y& Elsevier]

Abstract: The authors report on the performance of polymer-based light-emitting diodes, LEDs, using amorphous zinc oxide-doped indium oxide, IZO, as anode. In particular, LEDs with poly[(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] as electroluminescent layer and aluminium cathodes, show higher efficiency with this IZO anode (0.015cd/A) than with indium-tin oxide (ITO) (0.010cd/A). Inspite of the higher resistance of this IZO electrode, compared with ITO, the fact that it can be processed at lower temperatures and allows similar or even higher efficiency values for polymer LEDs make this material a good candidate for display and other optoelectronic applications. [Copyright &y& Elsevier]

Abstract: The characteristics of EL devices containing α-helical poly(l-glutamate) and having a carbazole side chain (PCELG) were found to strongly depend on the casting solvents. Among EL devices fabricated using chlorine-containing casting solvents such as 1,2-dichloroethane (DCE), 1,1,2,2-tetrachloroethane (TCE), chloroform (CHCl3), and monochlorobenzene (ϕ-Cl), the EL device fabricated using the DCE solvent exhibited the maximum luminance (65.8cd/m2). The difference between the threshold voltages of the devices ranged up to 6.0V, despite their fabrication by using solutions with the same composition ratio. The maximal efficiency of the devices fabricated using the DCE solvent was found to be 20 times greater than that of the devices fabricated using TCE solvents. A comparison of the current densities and voltages among devices fabricated using different casting solvents at their maximal efficiencies showed that the maximal efficiencies tended to significantly increase in the order TCE

Abstract: In this paper, we performed the design on the relative thickness of fluorescent–phosphorescent light emitters and evaluated the corresponding change of spectral characteristics of white organic light emitting diode (WOLED). Use of a 3-nm-thick separator composed of undoped phosphorescent host, which provides the confinement of singlet exciton, yields relatively well-defined broadband white emission. The optimized multilayers in WOLED comprises one of the simplest device structures among the reported fluorescent–phosphorescent hybrid WOLEDs, representing the Commission Internationale de l’Eclairage (CIE) 1931 chromaticity ranging from the nearly pure (0.30, 0.35) to warm white (0.35, 0.40) of 9.0–12.5cd/A (24,000cd/m2 at 12V bias). Although the presented efficiency data is not as high as the reports of others, design principles for a bright and stabilized three-peak-balanced white emission are discussed in detail, which will be beneficial for a step forwards in the development of broadband WOLED. [Copyright &y& Elsevier]

Abstract: Two benzothiazole derivatives, 4-(benzo[d]thiazol-2-yl)-N-(4-(benzo[d]thiazol-2-yl)phenyl)-N-phenylbenzenamine (BBPA) and 4-(benzo[d]thiazol-2-yl)-N-(4-(benzo[d]thiazol-2-yl)phenyl)-N-naphthylbenzenamine (BBNA), were synthesized and characterized. Electroluminescent devices with compound BBPA or BBNA as the blue-emitting layer were fabricated. The triple-layer device, in which BBPA acted as the blue-emitter, NPB as the hole-transporting layer and TPBI as the electron-transporting layer (Device 1), showed a current efficiency of 5.24cd/A, a power efficiency of 1.21lm/W and an external quantum efficiency of 2.88% at a driving current density of 20mA/cm2. The double-layer device with BBNA as the emitting layer and electron-transporting layer and NPB as the hole-transporting layer (Device 4) exhibited a maximum brightness of 1430cd/m2 at 13V with the CIE coordinates (0.21, 0.23). [Copyright &y& Elsevier]

Abstract: The novel spiro[fluorene-7,9′-benzofluorene]-based blue host material, 2-(10-phenylanthracene)-spiro[fluorene-7,9′-benzofluorene] (BH-3P), was successfully prepared by reacting 2-bromo-9,11-spiro[benzofluorene-fluorene] (3) with 9-phenylanthracene-10-boronic acid through the Suzuki reaction. Diphenyl-[4-(2-[1,1;4,1]terphenyl-4-yl-vinyl)-phenyl]-amine (BD-1), 2-[4′-(phenyl-4-vinylbenzeneamine)phenyl-spiro[fluorene-7,9′-benzofluorene] (BH-3BD) and 4-[2-naphthyl-4′ (phenyl-4-vinylbenzeneamine)]phenyl (BD-1N) were used as dopant materials. Blue OLEDs with the configuration of ITO/DNTPD/α-NPD/BH-3P:5% dopant/Alq3/Al–LiF were prepared from the BH-3P host and BD-1, BD-1N and BH-3BD dopants and they showed blue EL spectra at around 452nm at 7V and luminance efficiencies of 1.9–3.3cd/A. [Copyright &y& Elsevier]

Abstract: A series of seven ruthenium complexes with different ligands were synthesized and their optical, electrochemical and photoluminescent properties were characterized. Electroluminescent properties of these complexes were further evaluated using a light-emitting electrochemical cell with a configuration of indium tin oxide (ITO)/complex (100nm)/Au (100nm). Tunable photoluminescence (PL) and electroluminescence (EL) from 630 to 1040nm have been achieved by adjusting the LUMO and HOMO levels of ruthenium complexes. [Copyright &y& Elsevier]

Abstract: Efficient phosphorescent polymer light-emitting diode with poly(vinylcarbazole) (PVK) doped by two or three iridium complexes in single and bilayer structures are studied. With (tris-(2-4(4-toltyl) phenylpyridine) (Ir(mppy)3) as the green emitter and (1-phenylisoquinoline) (acetylacetonate) iridium(III) (Ir(piq)2) as the red emitter the efficiency is as high as 23cd/A with broad band emission from 500nm to 720nm. For white emission a second layer is added with blue emitter ((III) bis[(4,-6-di-fluorophenyl-pyridinato)N,C2] picolinate) (FIrpic) doped in PVK. White light containing three spectral peaks results with efficiency 8.1cd/A. As the second blue layer is replaced by the fluorescent (poly(9,9-dioctylfluorene)) (PFO) white emission with high color rendering index 86 is achieved. The efficiency is 5.7cd/A with peak luminance 8900cd/m2. For a given iridium complexes ratio the relative intensity of the green and red emission depends sensitively on the second blue layer. [Copyright &y& Elsevier]

Abstract: A series of new triscyclometalated iridium complexes Ir1–3 containing diphenylamino substituted phenylpyridine derivatives as ligands have been synthesized and characterized. Inter-ligand energy transfer and related emission color tuning were observed in these iridium complexes. The phosphorescence emission peaks red-shifted to longer wavelengths with increasing the conjugation length of the ligands. Heteroleptic Ir2 is highly amorphous and readily dissolved in a wide range of organic solvents. High-efficiency electrophosphorescent light-emitting diodes have been fabricated using iridium complexes Ir1–3 doped into hole-transporting host materials as the emitters. The device structure used in this study is ITO/PEDOT-PSS/Ir complex:host material/F-TBB/Alq3/LiF/Al, where F-TBB is morphologically stable 1,3,5-tris(4′-fluorobiphenyl-4-yl)benzene functioning as a hole- and exciton-blocking layer. It was found that the device performance was strongly influenced by a number of factors, such as the triplet energy and electrochemical properties of host materials, the energy offset between host and guest, and the balance of electron and hole in emitting layers. When doped in PVK host, amorphous Ir2 showed promising EL performance with a turn-on voltage of 5V, a maximum luminance >15,000cd/m2 at a driving voltage of 18V, and a peak current-efficiency of 21cd/A at a luminance of 1200cd/m2. [Copyright &y& Elsevier]

Abstract: Phosphorescent organic light-emitting diodes without hole blocking layer were developed by using a charge confining device structure which can confine excitons within light-emitting layer. Narrow triplet bandgap host material was sandwiched between wide triplet bandgap host materials and excitons could be effectively confined in narrow bandgap host light-emitting layer. The charge confining devices showed excellent device performances even without hole blocking layer because excitons were confined inside light-emitting layer. [Copyright &y& Elsevier]

Abstract: We synthesize a series of soluble phenylene-based electroluminescent (EL) polymers with deep blue emission by incorporations of dialkoxy groups (DRO-PPP) and alkoxy-phenyl group (EHB-PPP) on side chains as well as carbazole unit on main chain (EHB-PPP-Cz) using the Yamamoto coupling approach. The latter two modifications (EHB-PPP and EHB-PPP-Cz) lead to blue-shifts in absorption and emission maxima relative to DRO-PPP. In addition, the incorporation of carbazole as co-repeat-unit (EHB-PPP-Cz) leads to a raise of ionization potential (IP) to the level very close to that of the anode, PEDOT:PSS, to facilitate the hole injection. The maximum efficiency of the ITO/PEDOT:PSS/EHB-PPP-Cz/TPBI/CsF/Ca/Al device is 1.12cd/A with a stable deep blue EL with CIE (0.16, 0.05). [Copyright &y& Elsevier]

Abstract: A novel binuclear aluminum(III) complex with acylpyrazolone derivative as ligands, bis(salicylidene-o-aminophenol)-bis(4-benzoyl-3-methyl-1-phenyl-2-pyrazolin-5-one)-bis-aluminum(III) [Al2(saph)2(PMBP)2] was designed and synthesized. A detailed study was carried out on its thermal stability, photophysical, electrochemical and electroluminescent properties. It was found that the introduction of 4-benzoyl-3-methyl-1-phenyl-2-pyrazolin-5-one (PMBP) ligands improved the thermal stability remarkably. Organic light-emitting diodes (OLEDs) based on this Al complex as the sole emitter and the host for red dopant were fabricated. Bright green-yellow emission was observed from the device using Al2(saph)2(PMBP)2 as the emitter and the electron transporting layer. Pure red emission peaked at 632nm was obtained from the Al2(saph)2(PMBP)2 doped with DCJTB [4-(dicyanomethylene)-2-tertbutyl-6(1,1,7,7,-tetramethyljulolidyl-9-enyl)-4H-pyran] device with a luminance efficiency of 1.51cd/A at 200A/m2. No light from Al2(saph)2(PMBP)2 was found, indicating that the matched energy levels provide an efficient red emission system in Al2(saph)2(PMBP)2 device. Those results demonstrated that Al2(saph)2(PMBP)2 might be a promising material for OLEDs. [Copyright &y& Elsevier]

Abstract: A range of commercially available anionic dyes were successfully incorporated as dopants during the electrodeposition of poly(terthiophene) (P(TTh)). Photovoltaic testing revealed that the best photoelectrochemical cell (PEC) was based on P(TTh) doped with Sulforhodamine B, which showed short-circuit-current (I sc)=178μAcm−2, open-circuit-voltage (V oc)=318mV, fill-factor (FF)=29.6% and power-conversion-efficiency (PCE)=0.0334% under white light illumination intensity of 500Wm−2. Photocurrent action spectroscopy of the PECs based on dye-doped P(TTh)s prepared here, and of the PECs prepared in a previous study, showed that only a cationic dye directly contributed to photocurrent, while anionic dyes did not. It is proposed that these observations are due to attractive or repulsive electrostatic interactions between dyes and the electron acceptor I3 − at the polymer/electrolyte interface. [Copyright &y& Elsevier]

Abstract: A new red electroluminescent complex (2Fphen-bpy)Eu(DBM)3(2Fphen-bpy: 4-(2,4-difluorophenylene)-2,2′-bipyridine; DBM: dibenzoylmethanate) was designed and synthesized. X-ray single crystal structural analysis shows that the dihedral angles involving the difluorophenylene moiety and two pyridine rings of the 2,2′-bipyridine unit in (2Fphen-bpy)Eu(DBM)3 are 42° and 51.6°, indicant of non-conjugation between the two segments. The europium complex was incorporated into the doped electroluminescent device: ITO/TPD(40nm)/(2Fphen-bpy)Eu(DBM)3:CBP(30nm, 3%)/BCP(20nm)/Alq3(30nm)/LiF(1nm)/Al(100nm). At the brightness of 100cd/m2, the current and power efficiency are about 2.53cd/A and 0.79lm/W, respectively. In comparison with the inefficient control device using (2,2′-bipyridine)Eu(DBM)3 as the red emitter in the same configuration, the introduction of difluorophenylene moiety into the Eu(III) complex could possibly account for the improved performance of the title compound. [Copyright &y& Elsevier]

Abstract: The effect of C60 doped interlayer between poly(3,4-ethylenedioxythiophene:poly(styrenesulfonate) (PEDOT) and light emitting layer on the lifetime of phosphorescent organic light emitting diodes was investigated by changing the C60 content from 0% to 3%. Doping of C60 in 1,3,5-tris(N,N-bis-(4,5-methoxyphenyl)-aminophenyl)benzol (TDAPB) resulted in the increase of lifetime by more than 100% compared with lifetime of non-doped devices. [Copyright &y& Elsevier]

Abstract: Bis(arylquinoxalinyl)carbazole derivatives 9-phenyl-3,6-bis-(3-phenyl-quinoxalin-2-yl)-9H-carbazole (PPQC), 9-phenyl-3,6-bis-[3-(4-methoxy-phenyl)-quinoxalin-2-yl]-9H-carbazole (PMQC) and 9-phenyl-3,6-bis-(3-p-tolyl-quinoxalin-2-yl)-9H-carbazole (PTQC) were conveniently synthesized from the corresponding tetraone and o-phenylenediamine. Electroluminescent devices using PTQC as the dopant emitters were fabricated. These devices all emit saturated blue light from the PTQC doped layer. Device C that consists of CuPc (10nm)/TCTA (30nm)/PTQC:TPBI (7%, 30nm)/TPBI (40nm) shows the highest performance. The device emits blue light at 446nm with CIE values of (0.15, 0.08) and shows a maximum external quantum efficiency of 1.31%, current efficiency of 1.00cd/A, and brightness of 5067cd/m2. [Copyright &y& Elsevier]

Abstract: The organic light emitting devices (OLEDs) material tris-(8-hydroxyquinoline) aluminum (Alq3) is synthesized and deposited in thin film form by thermal evaporation on silicon and glass substrates. Thin films are studied for environmental related degradation. The light induced effects on Alq3 films exposed to white light in air and vacuum are characterized by atomic force microscopy (AFM) for surface morphology and phases present. The photoluminescence (PL) and spectroscopic ellipsometry (SE) techniques have been used to study optical properties. The AFM images, both topography and phase contrast, indicate a second phase with enhanced crystallinity for the vacuum exposed samples. This observation is supported by PL experiments. The phase with increased lifetime and hence enhanced crystallinity has also been found for vacuum exposed films by time correlated single photon counting (TCSPC) measurements. [Copyright &y& Elsevier]

Abstract: Monodisperse carbazole-based oligomers have been synthesized via Cormation by the modified Ullmann reaction. The full characterization of their structure is presented. These derivatives are highly thermally stable amorphous compounds with glass transition temperatures of 167–171°C and thermal decomposition temperatures of ca. 400°C. Amorphous films of the materials were fabricated and their hole-transporting properties were tested in a light emitting device with Alq3 as an electroluminescent and electron-transporting material. [Copyright &y& Elsevier]

Abstract: The synthesis of new molecules containing both electron and hole transporter units is reported. This class of compounds, named OC, may be used for assembling electroluminescent devices made by a single organic layer. The active moieties are the carbazole, as the hole transporter unit, and the oxadiazole, as the electron transporter unit. The chemical formulation and the complex geometry of the molecular frame allow good solubility in chlorinate solvents and the preparation of homogeneous films by spinning technique. Photoluminescence of molecules, both in solution and in film, occurs in the blue region of visible spectra, the exact peak position of emission depending on the pendants attached to the oxadiazole unit. The electroluminescence occurs in a higher wavelength region, with a blue-green emission. The electroluminescent devices consist in the simple sequence ITO–OC–Al and ITO–PEDOT–OC–Al. [Copyright &y& Elsevier]

Abstract: There has been a keen interest in metal benzothiazoles, and specifically for zinc benzothiazole for applications involving broad emission such as white light organic light emitting diodes. The broad emission characteristic is normally attributed to occurrence of exciplexes and is believed to further broaden in electroluminescence from a bilayer device. In order to understand possible role of molecular level interaction in photoluminescence (PL), we study PL decay dynamics of zinc benzothiazole powder, thin film and a virtual alloy with a hole transport material TPD (prepared by stacking very thin alternate layers of the two materials). We observe significant hastening of the PL decay from powder and ‘effective alloy’ to the thin film. To unravel the nature of changes in decay dynamics, we employ both least square fitting, and time domain spectroscopy known as time analyzed transient spectroscopy (TATS). The efficacy of the later procedure in obtaining insights is demonstrated. Our results indicate that inter molecular interaction in the condensed phase significantly influence the life time of the radiative species in this material. [Copyright &y& Elsevier]

Abstract: We investigate the possibility that high-energy singlet and triplet excited states with large electron–hole separations are generated in electron–hole recombination process, over and above the lowest singlet and triplet excitons. Using a time-dependent calculation of the interchain/intermolecular charge-transfer within model Hamiltonians that explicitly include electron–electron interactions between the π-electrons, we show that there occurs a bifurcation of the electron–hole recombination path in each of the two spin channels that leads to the generation of both the lowest energy exciton and a specific-high-energy charge-transfer state, with the matrix elements favoring the lowest energy exciton and the energy difference factor favoring the higher energy state, resulting in an enhancement of the singlet:triplet yield ratio above the value of 0.25 predicted from statistical considerations. [Copyright &y& Elsevier]

Abstract: Both electroluminescence (EL) and photoluminescence from conventional poly(di-n-octylfluorene) (PF8) light emitting diodes (LEDs) has been monitored in situ during thermal cycling at temperatures up to 410K. Even after the PF8 polymer undergoes a thermotropic phase transition to a liquid crystal phase these LEDs continue to operate although at reduced currents. This behavior is likely caused by changes in the hole transport layer and/or polymer interfaces and not by the phase transition itself. Overall EL output is diminished but PL measurements indicate no evidence of PF8 degradation. The step-wise thermal cycling of a working device produces a decrease in the relative EL efficiency at higher applied bias voltages but results in a pronounced EL efficiency increase at voltages near the device turn-on threshold. EL emission and measured device currents are both time- and temperature-dependent. [Copyright &y& Elsevier]

Abstract: Density functional calculations at the B3LYP/6-31G(d) level are used to predict the vibrational spectra for a series of substituted thiophenes and terthiophenes containing the emitter unit diethenylbenzene (DEB). The calculations show that cyano substitution induces non-planarity, particularly for the terthiophene compound. This was verified by the absorption and emission data, which suggest that the ground state is less planar than the excited state. The solution phase electronic spectroscopy reveals that some of the compounds are very emissive; however, CN substitution quenches this emission. Electroluminescent devices may be constructed using these emitter materials and it is found that the efficiency of the CNDEB compounds may be improved with the introduction of a different hole transporting layer. [Copyright &y& Elsevier]

Abstract: We have synthesized a spirobifluorene-based DPVBi [4,4′-bis(2,2-diphenylvinyl)-1,1′-biphenyl] analogue, DPVSBF [2,7-bis(2,2-diphenylvinyl)-9,9′-spirobifluorene], in which the bis(2,2-diphenylvinyl) groups are connected through the 2 and 7 positions of the spirobifluorene framework, and have characterized its thermal properties, electronic properties (viz. absorption and photoluminescence), and electrochemical behavior. The presence of the rigid spirobifluorene linkage imparts significant improvement in the material''s glass transition temperature and morphological stability, while preserving most of the photophysical and electronic properties of its non-spiro, biphenyl analogue, DPVBi. Organic electroluminescent devices having the structure ITO/NPB/DPVSBF/AlQ/LiF/Al display bright emissions with a λ max at 474nm (CIE coordinates: 0.16, 0.24) and exhibit maximum luminescence exceeding 40,000cd/m2. At a driving current density of 100mA/cm2 (6.4V), a luminance of 4110cd/m2 was obtained with external quantum efficiency of 2.54%, luminance efficiency of 4.1cd/A, and power efficiency of 2.0lm/W. Moreover, the DPVSBF-based device exhibits a 16-fold enhancement in the operation lifetime relative to that of a similar device based on DPVBi. [Copyright &y& Elsevier]

Abstract: Time-resolved photoluminescence (PL) of a red emitting dye, tetraphenylchlorin (TPC), doped in poly(methylmethacrylate) (PMMA) at various concentrations was studied to clarify the mechanism of concentration quenching often observed in organic electroluminescence devices. At doping concentrations lower than 10−2 mol/L, PL lifetimes of TPC were relatively constant (∼10ns) and equal to that of TPC in dilute solution. At doping concentrations higher than 10−2 mol/L, PL lifetime decreased rapidly with increasing concentration, down to 2ns at 8×10−2 mol/L. This decrease in PL lifetime was related to the concentration quenching of TPC monomer emission by the increasing number of TPC dimer sites formed at such higher concentrations. Our experimental results of concentration-dependence trapping agree fairly well with the theoretical model of trapping by dimers reported in literature. [Copyright &y& Elsevier]

Abstract: The new amorphous blue light emitting material, which is composed of biphenylenevinylene with α-phenyl as main unit and bulky triphenylsilyl as side units, is designed, synthesized and characterized. The tetraphenylsilane groups of tetrahedral molecular skelecton makes the material have high glass transition temperature of 130°C and good film quality. Blue organic light emitting device (OLED) employing this compound as the emitter exhibit the maximum luminescence of 4100cd/m2, the maximum external quantum efficiency of 0.7% and current efficiency of 1.67cd/A at 12.8V. [Copyright &y& Elsevier]

Abstract: We demonstrate highly efficient, vapor-deposited blue organic light-emitting diodes (OLEDs) operating at low voltage. For reaching deep-blue color, we used two new fluorophores, 9,10-bis(9,9′-spirobi[9H-fluorene]-2-yl)anthracene (Spiro-Anthracene) from Covion, and 4,4′-bis-(N,N-diphenylamino)-tetraphenyl (4P-TPD) from Syntec-Sensient, sandwiched in between p- and n-type doped wide band-gap transport layers and appropriate blocking layers. These p-i-n OLED devices show high luminance and efficiency at low operating voltages. Both dyes emit deep-blue light at color coordinates of x =0.15 and y =0.09 (4P-TPD) and x =0.15 and y =0.18 (Spiro-Anthracene). Optimized devices containing Spiro-Anthracene reach a luminance of 100 and 1000cd/m2 already at a voltage of 2.9 and 3.4V, respectively. At the same time, a deep-blue color with CIE color coordinates of x =0.14 and y=0.14 as well as good current efficiencies (3.9cd/A at 100cd/m2) and quantum efficiencies (3.7% at 100cd/m2) are reached, which shows that the concept of doped transport layers and appropriate fluorescent emitters can be applied successfully to the preparation of blue OLEDs. [Copyright &y& Elsevier]

Abstract: A family of rigid rod-like phenylethynylene oligomers and the homologue polymer were characterized by X-ray diffraction, DSC, UV–Vis and fluorescence spectroscopy. The pentamer as well as the heptamer exhibit liquid crystal properties characterized by a strong birefringence as observed by polarized microscopy, by DSC and by the X-ray diffraction pattern, where a lamellar ordered phase with layer spacing of 2.6nm was determined by Bragg''s equation. The optical absorption and emission spectra in CHCl3 showed that the conjugation increases with the oligomer length and the limit value is reached for the polymer, although a close saturation of the π–π conjugation is almost obtained for the heptamer. In a preliminary study, diodes were fabricated by spin coating thin films of pentamer and polymer on ITO electrodes and by subsequent vacuum deposition of aluminum cathodes. The (ITO/film/Al) devices showed intrinsic electroluminescent properties with low threshold voltage around 4V and yielding close to 10-6. These results are interesting in view of a further study of the optoelectronic properties of the whole family of oligomers. [Copyright &y& Elsevier]

Abstract: High efficiency electroluminescence (EL) in organic light emitting diodes (OLED) was achieved using cyclometallated platinum(II) complexes as new phosphorescent emitters. OLEDs containing bis[2-(2-thienyl)pyridine]platinum(II) [Pt(thpy)2] or bis[2-(5-trimethylsilanyl-2-thienyl)-pyridine]platinum(II) [Pt(thpy-SiMe3)2] show a high external EL quantum yield reaching 5.4 and 11.5% photon/electron, respectively. Both electroluminescent spectra fall in the “amber” color region defined by the automotive lighting standards; specifically the CIE coordinates are (0.58; 0.42) for Pt(thpy)2 and (0.60; 0.39) for Pt(thpy-SiMe3)2. [Copyright &y& Elsevier]

Abstract: We observed the electroluminescent behavior of films of the polydiacetylene poly[1,6-bis(3,6-dipalmitoyl-N-carbazolyl)-2,4-hexadiyne] (polyDPCHD) by preparing organic light-emitting diodes (OLED) based on a single emitting polymer layer. We measured their optical and electrical characteristics and obtained a typical power efficiency of 10-6. The observed rapid quenching of the electroluminescence was supposed to be related to the formation of charged traps enhanced both by local disorder of polymer chains and by current flow. [Copyright &y& Elsevier]

In this paper, we report on transient electroluminescence (EL) studies in (ITO/TPD/alloy/Alq3/Al) organic light emitting diodes. The alloy in the active layer is a co-evaporated mixture of TPD + Alq3 in the ratio TPD:Alq3 = 1:4. These results were compared with the transient EL response of a standard device (ITO/TPD/Alq3/Al). The EL response of the alloy device consists of two components – a fast component (10–20μs) and a slow component (200–300μs). It is shown that the slow component arises due to the leakage of electrons from the Alq3 layer into the alloy layer and subsequent exciton formation in the alloy layer. The magnitude of the fast component depends on the pulse repetition rate and temperature. This is shown to be related to the presence of deep traps in the alloy layer. The presence of deep traps is also confirmed by current transients in the alloy device. [Copyright &y& Elsevier]

A novel alternating conjugated polymer (C12-PPE-BT) containing phenylene-ethynylene and benzothiadiazole (BT) units (unless otherwise specified, C12-PPE-BT is represented that the BT ratio is 50% (mol%)) was synthesized by cross-coupling polycondensation with bis(triphenylphosphine)-dichloropalladium (Pd(PPh3)2Cl2) and phase transfer catalyst(PTC). C12-PPE-BT was characterized by 1H NMR, IR, TGA, DSC and elemental analysis. Its electrochemistry, photophysics and electroluminescence properties were discussed. The copolymer obtained possesses high thermal stability, high oxidation and reduction potentials, and high photoluminescence quantum yield. Devices based on C12-PPE-BT copolymer emit red light with λmax = 620nm. The emission of phenylene-ethynylene segments almost completely disappeared manifested that the intrachain and/or interchain energy transfer from phenylene-ethynylene segments to BT units occurred. [Copyright &y& Elsevier]

A novel hole injecting and transporting material, N,N-di(9-ethylcarbaz-3-yl)-3-methylaniline (DECMA), was prepared by one-step reaction for use in organic electroluminescent (EL) devices. Organic EL device with configuration of ITO/DECMA (60nm)/NPB (10nm)/Alq3 (60nm)/Mg:Ag/Ag turned on at 3.7V and displayed a brightness of 1150cdm-2 and a current efficiency of 5.5cdA-1 at the current density of 20mAcm-2, while a reference device with configuration of ITO/NPB (70nm)/Alq3 (60nm)/Mg:Ag/Ag turned on at 3.9V and exhibited a brightness of 500cdm-2 and a current efficiency of 2.4cdA-1 at the same current density. The lower turn on voltage and higher brightness and efficiency obtained in DECMA-containing device can be ascribed to the improved hole injection at anode/organic interface due to the low ionization potential of DECMA and the better balanced hole-electron recombination in emitting layer due to the moderate hole drift mobility of DECMA. [Copyright &y& Elsevier]

Current–voltage and impedance spectroscopy measurements have been carried out on the indium-tin-oxide (ITO)/1,4-bix-(9-anthylvinyl)-benzene (AVB)/Al light emitting diode. The impedance dependence of bias and frequency is discussed in term of the presence of a depletion layer in the bulk. Capacitance voltage measurements shows a linear behavior of C-2 with V which indicate the presence of a trap density less than ∼4×1016 cm-3. Current–voltage measurements indicate two mechanisms of conduction: a conduction limited by traps at lower forward bias and a SCL regime at higher forward voltages. In this device injection and conduction are dominated by holes. The hole mobility is determined using Mott–Gurney relation and was found to be on the order of 6.7×10-5 cm2/Vs. The device is accurately modeled, in reverse and forward biases and for frequency lied between 10 kHz and 10 MHz, as a single parallel resistor and capacitor network placed in series with a resistance. Finally, we present a qualitative description of the electroluminescence mechanism of the device. [Copyright &y& Elsevier]

Two luminescent polymers, poly[(2-methoxy-(5-(2-(4-oxyphenyl)-5-phenyl-1,3,4-oxadiazole)-hexyloxy))-1,4-phenylenevinylene-alt-2,5-didodecyloxy-1,4-phenylenevinylene] (P1) and poly[(2-methoxy-(5-(2-(4-oxyphenyl)-5-(4-biphenyl)-1,3,4-oxadiazole)-hexyloxy))-1,4-phenylenevinylene-alt-2,5-didodecyloxy-1,4-phenylenevinylene] (P2) was synthesized by the Heck coupling reaction. Hole blocking-electron transporting pendants, conjugated 1,3,4-oxadiazole (OXD) derivatives, is attached on the main chain via linear 1,6-hexamethylenedioxy chain. The band gap of both P1 and P2 were 2.12 eV and the maximum of photoluminescence (PL) of P1 and P2 appeared at 576 and 573 nm, respectively. Moreover, the maximum of electroluminescence (EL) of single layer device based on P1 and P2 showed at 583 and 580 nm, respectivley. These values are very close to those of poly(2-methoxy-5-ethylhexyloxy-1,4-pnenylenevinylene) (MEH-PPV). Relative PL quantum yield of P1 and P2 film were 1.9 and 2.0 times higher than that of MEH-PPV. In the PL and EL spectra, emission from CNST (1,2-diphenyl-2′-cyanoethene) pendants was not observed. These indicate that the energy transfer from OXD pendants to main chain takes place completely. In addition, OXD pendants did not affect the EL and PL maximum of the main chain of MEH-PPV. A single-layer EL device based on P1 and P2 had an efficiency of 0.1 cd/A at 300 mA/cm2 and 0.17 cd/A at 323 mA/cm2, respectively, which were significantly higher than that of MEH-PPV measured under the same conditions. From the energy levels figured out from optical and electrochemical data strongly supports that the OXD pendants have good hole blocking property and promote electron-hole (exciton) recombination process. [Copyright &y& Elsevier]