Laser Induced Thermal Imaging (LITI) allows for high-resolution patterning of a variety of materials that often cannot be patterned efficiently by other conventional techniques such as photolithography. Application of LITI towards patterning vacuum-coated OLED materials is particularly attractive because of high LITI patterning resolution and accuracy and good compatibility of vacuum-coated OLED materials. However, LITI may induce thermal transfer defects within OLED materials. We are developing methods to address these potential thermal defects while maintaining patterning quality, device operation efficiency, voltage, and lifetime. Recent results regarding optimization of LITI for patterning vacuum-coated OLEDs will be discussed.

Sony has commercialized a full-color OLED comprising a new red emissive material, which provides high performance and long operation lifetime. We have carried out systematic research and developed a promising material that has excellent properties for practical applications. This compound shows an absorption peak and a luminescence peak at 483 nm and 644 nm, respectively. The molar absorption coefficient is large (ε = 38,100 M^-1cm^-1 in 1,4-dioxane) and the fluorescence quantum yield is also very high (QY_f =0.82 in 1,4-dioxane). The glass transition temperature is as high as 135 °C. This compound offers thermally stable amorphous state in vacuum coating and is emissive even in single component films. We incorporated the new styryl compound in Sony's proprietary Super Top Emission technology and achieved outstanding brightness and wide color gamut comparable to the NTSC standard. The Super Top Emission consists of a top emitting device structure and color filters, which realize sufficient brightness and pure color at the same time without impairing the wide viewing angles. We obtained suitable device performance for practical use by tuning the layered structures. The emitting color is adjusted by optimizing the doping concentration of the styryl compound in the emitting layer and each thickness of the organic layers. We achieved the chromaticity (0.65, 0.35) in the CIE 1931 standard colorimetric system. The device operation lifetime exceeds 64,000 hours at the initial luminance 500 cd/m². We would also like to discuss the advantages over the conventional red emissive materials.

In this paper we report studies of gain in organic semiconductors, both in solution and the solid-state. OC₁C₁₀-PPV and F8BT solution amplifiers yielded gain of up to 40 dB and on average 30 dB across the spectral range 530-640 nm. We also present a conjugated polymer solid-state amplifier structure, which delivered amplification of 18 dB in a 300 μm channel length. The material used in the solid state amplifier was Dow RedF which had its high gain and low loss properties optimized by blending with F8BT.

We have studied energy transfer to a dioxolane-substituted pentacene derivative, 6,14-bis-(triisopropylsilylethynyl)-1,3,9,11-tetraoxa-dicyclopenta[b,m]pentacene (TP-5), from tris(8-hydroxyquin-8-olinato) aluminum(III) (Alq₃) by steady state and time-resolved photoluminescence (PL) spectroscopy. The Förster transfer radius is 27 Å, calculated from the fluorescence spectrum of Alq₃ and the absorption spectrum of TP-5. We find that pentacene emission dominates the PL spectra of TP-5:Alq₃ guest-host films, even at concentrations where the typical guest separation is significantly larger than the Förster transfer radius. Monte Carlo simulations of energy transfer to randomly dispersed guest molecules in the host matrix show that Förster-type energy transfer cannot completely account for the PL dynamics of the guest and host. Exciton diffusion within the Alq₃ host followed by fluorescence of the host molecules or energy transfer to the guest explains the PL spectra and dynamics.

Electroluminescence from conjugated polymers can be significantly improved by harnessing the energy of their nonemissive triplet states. Poly(2,7-dibenzosilole) has been prepared and its triplet energy has been measured as 2.14 eV, a figure that is slightly higher than that of polyfluorene (2.09 eV). Two new tris-cyclometalated iridium complexes with blue-to-green emission properties have been prepared and characterized.

In this study molecular doping in non-conjugated polymeric systems is utilized in order to obtain high efficiency electrophosphorescent light emitting devices (PHOLEDs). The device consists of a light emitting thin film layer composed of hole and electron transporting moieties dispersed in a polymer matrix of polyvinylcarbazole (PVK). Light emission is obtained by harvesting singlet as well as triplet excitons by means of a phosphorescent dye, Iridium (III) tris(2-(4-tolyl)pyridinato-N,C²) (Ir(m-ppy)₃), also dispersed in the polymer matrix. By incorporating a low conductivity polyethylene dioxythiophene-polystyrene-sulfonate (PEDOT) hole injection layer between the indium tin oxide transparent anode and the light emitting molecularly doped layer, the efficiency of these devices reaches values as high as 41 cd/A with a peak luminous efficacy of 28 lm/W. At the same time, triplet quenching by the hole transporting moiety as well as the electrodes are expected to be limiting the efficiency of these devices. In this paper we discuss several alternative device architectures studied in order to understand the factors affecting the device performance. In particular the effect of incorporating alternative hole transporting moieties and hole blocking layers are addressed.

We report effective enhancement of external quantum efficiency of phosphorescent organic light-emitting devices (OLEDs) with facially encumbered and bulky meso-aryl substituted Pt(II) porphyrins, probably suppressing non-radiative deactivation. The peak external quantum efficiencies (QEs) of the phosphorescent OLEDs with facially non-encumbered Pt(II) porphyrin 1, facially encumbered Pt(II) porphyrin 2, Pt(II) porphyrin 3 that bears bulkier 3,5-di-tert-butylphenyl substituents, and "doubly-decamethylene-strapped" Pt(II) porphyrin 4 were 1, 4.2, 7.3, and 8.2 %, respectively. The trend increasing performance in the order of 1 < 2 < 3 < 4 is related to facial encumbrance and steric bulkiness of Pt(II) porphyrins. Furthermore, in the case of Pt(II) porphyrin 4, it is considered that the "double straps" severely restrict rotational freedom of the meso-aryl substituents. The lifetimes for Pt(II) porphyrins 1-4 at a current density of 0.55 mA/cm² were 80, 103, 140, and 152 μs, respectively. The trend that the triplet lifetime becomes longer in the order of 1 < 2 < 3, 4 suggests that facial encumbrance and steric bulkiness suppress non-radiative deactivation. The triplet lifetimes of Pt(II) porphyrins 1-4 were all gradually shortened with increasing current densities, suggesting possible triplet-triplet annihilation and/or triplet-charge carrier recombination.

Currently, one of the most challenging applications for OLEDs is the full color display. The most energy-efficient way to realize light generation in OLEDs is by using phosphorescent emitters. Green and red emitters have already been demonstrated, but the search for blue emitting organic phosphorescent emitters with good color purity is still ongoing with arduous effort. Here we present our work with a new material developed at BASF which allows phosphorescent emission in the deep-blue spectral range. The emitter has an emission maximum at 400 nm, which gives CIE color coordinates of x = 0.16 and y = 0.06. An OLED device made with this new material shows a maximum external quantum efficiency of 1.5 %. The OLED was built in a three layer structure, with the emitting zone being a hybrid guest-host system. As host material we used the optically and electronically inert polymer poly-methyl-methacrylate (PMMA). Because of its lack of charge transport abilities we doped the host material with a high concentration of the triplet emitting material, i.e. the emitter itself is also used as charge transport material.

The use of organic light-emitting diodes (OLEDs) for large area general lighting purposes is gaining increasing interest during the recent years. Especially small molecule based OLEDs have already shown their potential for future applications. For white light emission OLEDs, power efficiencies exceeding that of incandescent bulbs could already be demonstrated, however additional improvements are needed to further mature the technology allowing for commercial applications as general purpose illuminating sources. Ultimately the efficiencies of fluorescent tubes should be reached or even excelled, a goal which could already be achieved in the past for green OLEDs.¹ In this publication the authors will present highly efficient white OLEDs based on an intentional doping of the charge carrier transport layers and the usage of different state of the art emission principles. This presentation will compare white PIN-OLEDs based on phosphorescent emitters, fluorescent emitters and stacked OLEDs. It will be demonstrated that the reduction of the operating voltage by the use of intentionally doped transport layers leads to very high power efficiencies for white OLEDs, demonstrating power efficiencies of well above 20 lm/W @ 1000 cd/m². The color rendering properties of the emitted light is very high and CRIs between 85 and 95 are achieved, therefore the requirements for standard applications in the field of lighting applications could be clearly fulfilled. The color coordinates of the light emission can be tuned within a wide range through the implementation of minor structural changes.

A 6"x6" white lighting panel consisting of red, green and blue colored stripes of OLEDs emits >100 lm of optical power and has a maximum energy efficacy of 30 lm/W. Each colored stripe contains 7 serially connected OLEDs having an area of 1.37 cm², and there are 4 stripes per color, so there is a total of 84 devices. The external quantum efficiency of the red and blue OLEDs exceeds 20% and the blue OLED efficiency exceeds 5% when operated above 100 nits. Such high quantum efficiencies are achieved with an OLED architecture consisting of electrophosphorescent dopants, and at least four organic thin films layers: a hole injection layer, a hole transport layer, an emissive layer, a blocking layer, and an electron transport layer. The color coordinates of the panel can be varied between the constituent red, green, and blue color component coordinates of (0.14, 0.17), (0.31, 0.64), and (0.62, 0.38), respectively, by adjusting the intensity of each primary colors. Panel power efficiencies were measured at correlated color temperatures between 2,900 K and 5,700K, and the color rendering index was >80 in all cases because of the broad spectral output of the combined colors.

OLEDs for lighting applications are gaining increasing attention due to the possibility to produce large area, 2-dimensional light sources. In contrast to the existing technology e.g. based on white inorganic LEDs this offers a completely new freedom in design for applications of next generation lighting. Today, different approaches to achieve white broadband emission for organic lighting solutions are investigated ranging from devices with blue emission in combination with conversion layers to RGB-color by lateral patterning with the support of active color tunability. Within this contribution we present results of broadband emitting copolymers to achieve white emission. New requirements arising from the shift of OLEDs in a display configuration to those for lighting applications are discussed with focus on the electro-optical behavior. Furthermore, we describe challenges that result from using large active areas and investigate ways to improve large area lighting tiles.

This paper describes Eastman Kodak Company's commercialization efforts to develop new materials and formulations for monochrome and full-color displays. We have found a new set of materials, and combinations thereof, that improve luminance efficiency, lower drive voltage, and increase the operational stability of OLED devices. We report the developments in formulations for blue and white OLEDs based on fluorescent dopants that provide lifetimes exceeding 10,000 hours for blue, and 50,000 hours for white OLEDs at a starting luminance level of 1000 cd/m². A red formulation, based on a fluorescent dopant using a new host, is shown to give a record luminance efficiency of 7.8 cd/A combined with excellent color and lifetime. We have found a phosphorescent red-emitting device using a novel host material that gives an excellent efficiency of 9.6 lm/W. Further progress has been made in a new electron-transport layer to reduce display drive voltage, and thus reduce power consumption, while simultaneously increasing operational stability. We have compared this performance with currently available systems.

Poly(p-Phenylene Vinylene) derivatives are synthesized mostly making use of the polymerization behavior of p-quinodimethane systems. Over the last forty years different synthetic routes have been developed, e.g. Wessling, Gilch, Xanthate and Sulphinyl route. For all these routes mechanistic studies are rather scarce and lead to a controversy between two possible mechanisms: anionic and radical polymerization. In this contribution it becomes clear that high molecular weight materials are associated with a self-initiated radical chain polymerization and low molecular weight materials are obtained via an anionic mechanism. This will be demonstrated for the model system in which a sulphinyl pre-monomer is polymerized in N-Methyl-Pyrrolidone. In this model system both these mechanisms are competing with each other. The observed effects on the product distribution of concentration of reagents, temperature and order in which the reagents are added, are consistent with the conclusion above. The question whether living polymerization can occur will be addressed for the radical mechanism. An experiment with a set of sequential polymerizations gives rise to an evolution of molecular weight consistent with the effect of simple dilution of the reaction medium. The conclusion is that a termination reaction is active, which can be identified as related to traces of oxygen. In these conditions the synthesis of block-type copolymers can not be achieved. For the anionic mechanism an argumentation against such possibility will be presented on the basis of relative acidities.

We measured delayed electroluminescence in abrupt heterojunction undoped and doped small molecule organic light emitting diodes (OLEDs) based on NPB and AlQ₃ hole and electron transport and emitter molecules, after the excitation currents are switched off and reverse bias applied to the sample. The experiments indicate that delayed light emission is a result of two distinct processes: emissive excited singlet state generation by either triplet-triplet annihilation or recombination of trapped positive and negative charges in the device. Under reverse device bias these two mechanisms have distinctly different signatures. Undoped devices show dominant light emission contribution from triplet-triplet annihilation, while in rubrene and coumarine doped devices delayed light emission comes predominantly from recombination of trapped charge. Therefore these molecules act as recombination centers when doped into AlQ₃.

We demonstrate very low threshold laser oscillation (E_th= 0.78 ±0.5 μJ/cm²) from an organic semiconductor thin film employing 2,5-bis(p-(N-phenyl-N-(m-tolyl)amino) styryl)benzene (BSB-Me) as an active gain medium equipped with a second order distributed feedback resonator. Further, we demonstrate laser oscillation under optical excitation from an organic light emitting device equipped with transparent ITO hole and electron injection electrodes. In addition, we demonstrate injection and transport of high current density over J > 500 A/cm² in an organic light emitting diode using highly thermal conductive substrates and a small electrode under short pulse voltage excitation.

The properties of electrically pumped organic laser devices are investigated by the self consistent numerical solution of the spatially inhomogeneous laser rate equations coupled to a drift-diffusion model for the electrons, holes and singlet excitons. By fully taking into account the effect of stimulated emission on the exciton population, we determine the spatial and temporal evolution of the photon density in organic multilayer structures. We apply the model to calculate laser threshold current densities and investigate transient phenomena like the delay of radiation onset. By performing systematic parameter variations, we derive design rules for potential organic laser diode structures.

Conjugated polymers with a stabilized blue emission are of importance for the realization of full-color displays using polymer light-emitting diodes. We report a new class of blue-emitting polymers utilizing a new back-bone, poly(2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta [def] phenanthrene)) (PCPP). This material emits a stabilized, efficient blueelectroluminescence(EL) without exhibiting any peak in the long wavelength region (green region) even after prolonged annealing for 18 hours at an elevated temperature of 150°C in air. This attributes to the chemical structure of this new polymer. The backbone of PCPP intrinsically inhibits the formation of the keto-defects mainly responsible for the degradation to green color in typical poly(fluorine) type materials, thereby stabilizing the blue EL emission in the devices.

We present highly efficient, low voltage top emitting organic light-emitting diodes (OLEDs) employing the same material (Ag) for both anode and cathode. Benefiting from doped charge carrier injection and transport layers (p-i-n structure) the diodes show comparable or even better electric characteristics than similar bottom emission OLEDs although the work function of the electrodes in the top emission OLEDs and the HOMO/LUMO location of the transport materials do not coincide. A green top emitting OLED with an Ir(ppy)₃ doped double emission layer (D-EML) is demonstrated showing an efficiency of 50 cd/A at a brightness of 1000 cd/m² and at the same time needing a very low driving voltage of only 2.85 V for 1000 cd/m². By putting an additional organic capping layer on top of the cathode, the optical structure of the device can be tuned and the efficiency of the diodes can be further improved to a maximum efficiency of 78 cd/A at a brightness of 1000 cd/m². Using the same capping strategy, efficient phosphorescent red and fluorescent blue top emitting OLEDs are demonstrated with efficiencies at 1000 cd/m² as high as 13.6 cd/A and 8.6 cd/A, respectively.

We report for the first time the bipolar transport properties of the LUMATION* 1300 Series green emitting polymer investigated by means of admittance spectroscopy. Analysis of the inductive response in single carrier polymer diodes yields electron and hole mobilities which are in excellent agreement with the results of independent measurements. Admittance measurements in dual injection diodes provide evidence that the dual injection diodes operate in spacecharge-limited regime, indicative of strong recombination within the material. Our results provide strong evidence that the space-charge-related admittance response of dual carrier diodes is dominated by combined electron-hole response, which corresponds to the sum of electron and hole mobilities. This implies that electron and hole mobilities cannot be obtained separately from admittance measurements in space-charge-limited dual carrier devices.

Although organic light emitting diodes are generally well characterized, their mechanism of decay, e.g. formation of black spots, is still not fully understood. Here we present a new technique allowing for deeper insight into the degradation process of an OLED by measuring its photovoltaic properties. The results show the possibility to record maps of crucial photovoltaic values with a lateral resolution of 50 microns. Based on these results, we propose a mechanism for the decay process. Black spots in the device are formed during the fabrication process, and the lifetime is determined by the active materials' chemical stability.

Two types of flexible organic light-emitting diode (OLED) displays are described. One is a passive matrix (PM) display with 128 (RGB) x 72 pixels, and the other is an active-matrix (AM) panel with 4 x 4 green pixels using organic thin-film transistors (OTFTs). The emitting layer of these displays is based on high-efficiency phosphorescent materials. The PMOLED display showed a clear color video image even when it was bent. The AMOLED panel could actively drive the OLED pixels. These results suggest that the OTFT-driven OLED display would be a promising candidate for rollable mobile displays.

The rapid growth of OLEDs will occur when device performance, particularly lifetime, and production costs are optimized. Plextronics Inc. is using a versatile technology platform to develop HIL technology that will address critical degradation factors of solution processed OLEDs. In particular, significant effort has been applied to understanding the impact of inputs including the inherently conductive polymer, dopant system, solvent system, and additional functional additives, on resulting HIL film properties, which are presented here.

Charge carrier drift mobilities of a series of hole-transporting amorphous molecular materials have been determined by a time-of-flight method. Electric-field and temperature dependencies of carrier mobilities have been analyzed in terms of the disorder formalism, and charge transport in amorphous molecular materials is discussed in relation to molecular structures. Hole-transporting amorphous molecular materials with high mobilities of the order of 10^-2cm²V^-1s^-1 have been developed.

The transport of charge carriers in polymer-based Organic Light-Emitting Diodes (OLEDs) as determined by the hopping mobility is an important factor influencing both lifetime and performance of OLED devices. It is strongly dependent on the density and energetic distribution of trap states in the polymer material. Especially in multi-component copolymers single functional groups can act as hole or electron traps determining the optical and electrical characteristics of the device. Transient measurements of the charge carrier mobility together with steady-state current-voltage characteristics are used to investigate the behavior of three blue polyspiro-based light-emitting polymers (LEP) with varying compositions. The first material is a simple homopolymer, the second adds a hole transporting component which is copolymerized into the backbone and the third, most complex, additionally includes a blue chromophore. With some of the added components acting as charge carrier traps the electrical behaviour of the diodes changes significantly.

We studied the hole mobility of molecularly doped hole transport layer (HTL), 4,4'-bis[N-(1-napthyl)-N-phenyl-amino]-biphenyl (α-NPD), as a function of the doping concentration of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) by employing the time-of-flight photoconductivity (TOF-PC) technique. The hole transport is non-dispersive for α-NPD and the hole mobility of pristine α-NPD is about 10^-3 cm²/Vs at room temperature. However, the hole mobility decreases with the BCP doping concentration in α-NPD. We characterized the current-voltage-luminance dependence, the EL quantum efficiency, and transient EL response for the devices of ITO/doped α-NPD/Alq₃/LiF/Al. The devices with the BCP doped α-NPD show higher EL efficiency compared with the device with pristine α-NPD. The reduced hole mobility in the BCP doped α-NPD enhances the electron-hole balance, resulting in an increased EL efficiency.

Fluorene-based materials, such as polyfluorenes or oligofluorenes, are conventionally well known as efficient blue emitting materials. Intriguingly, it is recently unveiled that ter(9,9-diarylfluorene)s also exhibit efficient unusual nondispersive bipolar carrier-transport characteristics and high carrier mobilities of >10^-3 cm²/Vs for both holes and electrons in the amorphous state. Making use of convenient substitution on C9 of fluorenes and corresponding variety in molecular structures and physical properties, in this work we systematically investigate influences of molecular structures, such as dialkyl-substitution vs. diaryl-substitution and oligomer length etc., on charge transport of oligofluorenes. Furthermore, utilizing liquid-crystalline properties of oligofluorenes with appropriate substitutions, comparative studies of carrier transport of oligofluornes in both vacuum-deposited amorphous states and aligned liquid-crystal glass states are also performed. Insights on intermolecular charge transport derived from the experimental observations and theoretical examinations are then discussed accordingly.

In this report, we have investigated electroluminsecence (EL) characteristics and field-induced recovery of organic light-emitting devices (OLEDs) with a mixed emitting layer (EML). The mixed EML which is composed of a mixture of a hole transport layer (HTL), N,N'-diphenyl-N,N'-bis(1,1'-biphenyl)-4,4'-diamine (NPB), and an electron transport layer (ETL), bis(10-hydroxybenzo[h]quinolinato) beryllium (Bebq₂), was fabricated by co-evaporation. Evident recovery of luminance-voltage characteristic was observed in the mixed device. It is explained by a dipole rearrangement model. The lifetime of this mixed layer OLED can reach 348 min. with initial luminance of 11,000 cd/m² which is two times better that of the comparable heterojunction device.

A full color 2.2" passive matrix organic light-emitting diodes (OLEDs) with 128 (RGB) ^* 160 pixels was developed. The display features that driving circuit can transform 18 bits gray-scale data from a PC to the OLED panel via a DVI channel. The size of the pixel was 240μm×240μm, while that of mono sub-pixel is 190μm×45μm. The lifetime of panel was estimated over 5000h because of the use of dual-scan driving technology, and the power consumption of the display was 300mw about when the average luminance of panel reach 40cd/m².

Tris(8-hydroxyquinoline) aluminum (Alq₃) is one of the most commonly used electron transporting and luminescent materials for organic light emitting diodes (OLEDs). It is thermally and morphologically stable to evaporate into thin films and it is a good green emitter. Due to its importance in OLEDs, the properties of Alq₃ have been extensively studied. Most of the studies, however, were concentrated on the single crystals, powder or thin films of Alq₃. Recently, synthesis of Alq₃ nanostructures, such as nanoparticles and nanowires, has been reported. Nanostructures have been attracting increasing attention because they may have new optical, electronic, magnetic, and mechanical properties compared with those of bulk materials. In this work, we reported synthesis of Alq₃ nanowires by heating Alq₃ powder in a gas flow. The nanowires were grown on glass substrates which were located in the downstream. The obtained nanostructures were characterized by scanning electron microscopy (SEM) and photoluminescence (PL). The effect of substrate temperatures, fabrication system geometry (i.e. source to substrate distance), the choice of gas, and gas flow rate on the resulting nanostructures were investigated. It is found that the synthesis conditions had significant effect on the morphologies of the resulting nanostructures, but the PL showed no significant dependence on the morphology.

One of the serious problems in polymer light-emitting diodes (PLEDs) is the difficulty of electron injection in the current PLEDs device of anode/polymer/cathode geometry. This is particularly true for the case of aluminum (Al) electrode. The work function of Al is too high to match with the Lowest Unoccupied Molecular Orbit (LUMO) level of the luminescent polymers, thereby lowering the device efficiency. In this work, by introducing solution-based titanium oxide (TiO_x) thin film as an electron injection layer between the polymer and Al electrode, we demonstrate that the devices exhibit an enhanced efficiency. The TiO_x layer reduces the barrier height between the polymer and aluminum (Al) cathode, thereby facilitating the electron injection in the devices.

The measurement and analysis of the current-voltage characteristics of a liquid-crystalline organic semiconductor 2-(4'-Octyphenyl)-6-dodecyloxynaphthalene (8-PNP-O12) in contact with electrodes of Pt, Au, ITO, Cr, and Al in the order of work function revealed that the injection of positive holes from the electrodes of Pt, Au, and ITO to 8-PNP-O12 took place according to the Schottky model, and that an electric double layers was formed at the interface between each of these electrodes and 8-PNP-O12, making it difficult to inject positive holes from the former to the latter.

Systematic investigations of luminescence lifetimes of organic phenylene nanofibers are presented as a function of intrinsic parameters such as morphology or bleaching factor as well as extrinsic parameters such as substrate material, coating or excitation intensity. By varying either one of these parameters, the decay times of the electronic excitation can be varied. This should have a strong influence on the efficiency of nanolasing, which is observed by increasing the excitation intensity of a femtosecond pump laser. Lasing action starts at pump fluences as low as a few μJ/cm² per pulse. In ensemble measurements, the number of lasing modes depends strongly on the density of contributing nanofibers. In spatially resolved measurements, the nonlinear optical response of individual nanofibers is investigated. This enables us to make a correlation between the morphological features of the nanofibers, as deduced from atomic-force microscopy, and their lasing properties.

Electroluminescent bipolar small molecules have been attracted with great interests recently. They are found to exhibit many interesting features such as (i) reducing the structural complexity of organic light emitting diodes (OLEDs) from multilayer heterojunction to monolayer homojunction devices; (ii) offering molecular p/n junction, and (iii) minimizing the formation of exciplexes. In this paper, the optical and electrical properties of novel oxadiazole-triphenylamine derivatives will be investigated. The derivatives are N-phenyl-N-(4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl)phenylamine (POT) and N-phenyl-N-(4-(5-p-tolyl-1,3,4-oxadiazol-2-yl)phenyl)phenylamine (m-POT). The absolute absorption coefficient and refractive index have been investigated by ellipsometry and modeling. The electron mobility of POT at room temperature has been studied. The results show that the derivatives have bipolar characteristics. The electron-transporting properties of POT is better than that of m-POT. The EL emission peaks of POT and m-POT are the same at 435nm which match with their photoluminescent (PL) peaks.

The performance of blue emitting OLED devices, using a polyspiro as blue light emitting polymer, were studied as a function of the conductivity of a novel hybrid hole injection material. The hole injection material is based on a polyarylamine using a molecular magnet as oxidant. The charge density and the luminance of the devices changed considerably with increasing conductivity of the hole injection layer. The change in device performance can be attributed to a change from a hole limited device to a balanced charge carrier device and eventually to an electron limited device. The performance of the optimized device configuration is significantly improved with respect to a device making use of PEDOT:PSS as the hole injection layer reaching efficacies of 3.5 cd/A at 5000 cd/m².

Polyhedral oligomeric silsesquioxane having carbazole moiety, octakis[2-(carbazol-9-yl)ethyldimethylsiloxy]silsesquioxane (POSS-Cz), was synthesized by hydrosilylation reaction between octakis(dimethylsiloxy)silsesquioxane and 9-vinylcarbazole in the presence of platinum catalyst, and can be characterized by ¹H, ¹³C, ²⁹Si NMR, IR, and MALDI-TOF MS spectroscopies. POSS-Cz is soluble in common organic solvents. Comparison of thermal, electrochemical, and optical properties of POSS-Cz with those of 9-ethylcarbazole (EtCz) and poly(9-vinylcarbazole) (PVCz) revealed that electrochemical and optical properties of POSS-Cz are similar to those of EtCz, but POSS-Cz shows glassy state similarly to PVCz.

Semiconducting conjugated polymers have recently attracted significant interest as amplifying media for solid-state lasers due to their functional photo-physical properties and simple fabrication. Distributed feedback (DFB) cavities are proving to be the most attractive for polymer lasers, since they can combine the properties of transverse optical pumping, low threshold and practical output beams. To date, in most polymer DFB lasers the feedback is provided by second order diffraction. This has the advantage of surface emission, though it also imposes extensive scattering losses. In this work, we present the use of alternative structures that attempt to reduce the threshold of polymer DFB lasers, and also achieve dual wavelength operation. The former was addressed with cavities formed by alternative symmetries of the Brillouin zone of a square lattice. Using the diagonal ΓM symmetry first order feedback was attained. The threshold energy was thus reduced by almost an order of magnitude as compared with the more commonly used ΓX symmetry of second order square gratings. Finally, we show that two lasing wavelengths may be set independently in a semiconducting polymer laser by using a doubly periodic (i.e. Moiré) DFB grating.

In this paper, we demonstrated methods for determining the recombination zone in a mixed-host (MH) organic light-emitting device (OLED). The host of the emitting layer material in this device consists of a hole transport layer and an electron transport layer fabricated by co-evaporation. By comparing the spectra shift between bilayer and MH OLEDs, the recombination position with different mixing concentration can be determined. It showed the recombination zone shifts from the anode to the cathode side with increasing NPB mixing ratio.

We presented detailed spectroscopic data obtained from Nd³⁺ pyridine-2,6-dicarboxylic acid based complexes in which the 4-position of the pyridine ring has been substituted with OH and Cl. In each case the ligands formed stable complexes with the Nd³⁺ ion without the requirement for any additional 'neutral' ligand to satisfy the 8-9 coordination requirement of the lanthanide ion. Photoluminescence is observed from both the ligand (centered ~700 nm) and the Nd³⁺ ion (at ~900 nm, 1064 nm, and 1320 nm due to the ⁴F_3/2 → ⁴I_9/2, ⁴F_3/2 → ⁴I_11/2, and ⁴F_13/2 → ⁴I_9/2 transitions respectively) following excitation in the low energy tail of the ligand π → π* absorption. The intensity of the ligand emission and sensitized Nd³⁺ emission was found to be dependent on the substituted 4-position of the pyridine ring. The origin of the observed phenomena are discussed in relation to the energy transfer process from ligand to Nd³⁺ ion and the nonradiative relaxation of the sensitized Nd³⁺ ion. These results suggest that further modification of the ligand through complete halogenation and/or addition of other functional groups may provide an attractive route to obtaining an efficient near-infrared emitting organolanthanide complex.

In this paper, we demonstrate device performances with cesium (Cs) doped in oxadiazole (OXD) derivatives as a metal-doped electron transport layer (MD-ETL). Cs is a heavy alkali atom and difficult to diffuse in an organic matrix. The metal quenching effect is therefore reduced in a long-term operation. Three different kinds of OXD-based organic materials were used. However, only one kind of OXDs can effectively improve the device performances. Such a host material exhibits advantages of high glass transition temperature (Tg) of 147 °C. The average roughness of the thin film is small hence the leakage current of the corresponding OLED devices is low. By using a highly reflective and conductive silver cathode, an OLED with a 2.59 V reduction in driving voltage, a 47.3% increase in current efficiency, and a 3.14 times enhancement in operation lifetime was demonstrated.

We report here on the results of the characterization of a novel -OPhCN substituted thiophenic monomer, and of the obtained copolymers between the latter and the plastifying comonomer 3-hexylthiophene. The polymer evidences an excellent filmability from various organic solvents as well as an enhanced photoluminescence. The characteristics of the polymer were characterized by FTIR and XRD as well as photoluminescence. A bandgap of 2.0eV was obtained which corresponds to orange emission. Furthermore, a single layer organic device was fabricated and resulted in bright stable electroluminescence at room temperature. All of the results indicate that this polymer is a promising emissive material for application in light-emitting devices (LEDs).

Non-doping white organic light-emitting devices (WOLEDs) based on an ultrathin yellow-emitting layer of rubrene inserted between the blue-emitting layer 4,4'-bis(2,2'-diphenylvinyl)-1,1'-biphenyl (DPVBi) and the electron transport layer tris-(8-hydroxyquinoline)aluminum (Alq₃) fabricated by combinatorial sliding shutter technique are reported. Three of the the sixteen devices made had Commission Internationale de l'Eclairage (CIE) coordinates within the white region at 8 - 16 V, ranging from (0.31, 0.38) to (0.34, 0.42). All three devices had a 5-nm thickness of DPVBi layer and an ultrathin rubrene layer of thickness of 0.05-, 0.10-, and 0.15 nm, respectively. A maximum luminance of 12,900 cd/m² at 17 V and an efficiency of 5.5 cd/A at 8.5 V were obtained in the devices with 0.05 nm rubrene layer. These devices can be fabricated rather easily due to their simple device structure and they are very appealing to low-cost general lighting applications.

We analyzed the experimental time-of-flight data for photoinjected holes in two smectic liquid crystals, the first consisting of a phenylnaphthalene derivative 8PNPO12, and the second consisting of a biphenyl derivative 6OBP6. We fit the time of flight transients for different electric field strengths to a multiple trapping model (MTM). From these fits we determined the distribution of trap depths, under the assumption that (i) linear response is valid, and (ii) the trap release rates are independent of field.

In this paper, the effects of hole injection layer (HIL) on the performance of typically used tris-(8-hydroxyquinoline) aluminum (Alq₃) based OLEDs have been investigated. Three different HIL materials were used: copper phthalocyanine (CuPc), magnesium phthalocyanine (MgPc) and zinc phthalocyanine (ZnPc). The Metallophthalocyanines (MPcs) will be used to construct single hole injection layer (HIL) and double HIL (d-HIL). In the OLEDs, Alq₃ acts as the emitting layer and electron transport layer. Although d-HIL structures show higher efficiency than that of the reference device, the highest current efficiency ~ 4.02 cd/A corresponds to the 15 nm ZnPc HIL device. Compared to an current efficiency of ~3.29 cd/A and a power efficiency of ~0.99 lm/W (at 100 cd/m² luminance) of the reference device, an 15 nm ZnPc HIL device has ~22% higher current efficiency and ~67% higher power efficiency. The reasons for the improvements will be discussed.

We report the observation of cathodoluminescence (CL) of organic multilayers of tris-(8-hydroxyquinoline) aluminium (Alq3) and 2- (4biphenyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole (PBD) deposited on ITO-coated glass, with and without hole transport layer and compare it with electroluminescence (EL) from similar devices. Excitation of the CL of such multilayer organic anodes was accomplished by low energy electrons field emitted by single walled carbon nanotube cathodes. The dependence of CL spectrum and intensity on voltage (V), current (I), type of transport layer and the cathode-anode geometry has been studied. We propose carbon nanotubes as efficient cathodes for stable CL emission from multi-layer anodes at small cathode-anode separations. The role of hole-transport layer is also discussed.

By engineering a new cohosting system of tris(8-hydroxyquinoline) and 4,7-diphenyl-1,10-phenanthroline in the electron transport layer, the current efficiency of the organic light emitting diode is improved by more than 20% while the bias is reduced by ~40% as compared to the device with a single host of Alq₃ as the electron transport layer. The maximum luminance is over 16000 cd/m² at the bias of 22V and the current of 475mA/cm², which is ~73% higher than the single host Alq₃ device without optimizing the layer thickness. The lifetime under ambient environment is enhanced by a factor of ~1.8. The reasons for the improvement will be investigated. The results strongly indicate that the knowledge of bulk conductivity engineering of organic n-type transporters shows practical significance in OLED applications.

In this paper, we demonstrate a phosphorescent organic light emitting device (PHOLED) with low turn-on voltage by using a n-type organic material as the host of the emitting layer (EML) doped with green emitting complex, fac tris(2-phenylpyridine) iridium Ir(ppy)₃. This material exhibits high glass transition temperature (over 200 °C) that may help to elongate the operation lifetime. We compare our devices to the classical 4,4'-N,N'-dicarbazole-biphenyl (CBP) based green device. Driving voltage of the CBP and the new-host based OLED is 16 and 11 V with the current density of 100mA/cm², respectively. The lower driving voltage of the new-host based device comes from the lower HOMO value, i.e. 5.7 eV, which is nearly the same as that of NPB. The current efficiency at 10000 cd/m² is slightly decreased from 24 to 21 cd/A. However, the power efficiency is increased from 5 to 6 lm/W.

Highly efficient blue and white light-emitting organic electroluminescent devices have been fabricated by evaporation of small molecules. The emitting material of the blue multilayer EL devices (ITO/CuPc/α-NPB/Doped DPVBi/Alq3/LiF/Al) is based on a DPVBi (4,4'-bis(2,2-diphenylvinyl)biphenyl) matrix. In order to increase the EL efficiency and to improve the blue colour, this emitting layer is doped with a derivative of distyryl biphenyl molecules: PR3491. After the optimisation of the percentage of dopant, quantum and current efficiencies of 5.7 % and 7 cd/A, respectively, are obtained for a deep blue diode with CIE chromaticity coordinates of (0.15, 0.14). White diodes have been also realized doping the DPVBi emitter or the α-NPB hole transporting layer (HTL) of the previous structure with rubrene. A double doped system has been finally realized from the deep blue diode (DPVBi doped with PR3491) and with rubrene in the HTL layer. After tuning the two percentages of dopant in order to balance the blue and the yellow contribution to the diode emission, a fairly pure white emission is obtained with CIE coordinates of (0.31, 0.34) and external efficiencies of 3.4 % and 8.7 cd/A at 10 mA/cm².

A simple convergent procedure, involving the Diels-Alder reaction between 2,3,4,5-tetraphenylcyclopentadienone with an acetylene-substituted 2-phenylpyridine and subsequent complexation with iridium(III), has been developed for the formation of highly branched phosphorescent dendrimers. The procedure is demonstrated with the preparation of a first generation dendrimer composed of a fac-tris(2-phenylpyridyl)iridium(III) core with a single dendron attached to phenyl ring of each of the ligands. Each dendron is comprised of a branching phenyl unit with a further four phenyl groups attached. The lack of surface groups on the dendrons was found to reduce solubility of the dendrimers and allow strong intermolecular interactions of the emissive and electroactive cores in neat films. This was evidenced by a decrease in the photoluminescence quantum yield in going from solution to the solid state.

The concept of tandem organic light-emitting devices (OLEDs) provides a pathway for developing highly stable and efficient OLEDs. The connecting structure that bridges adjacent light-emitting units, substantially affects the device performance of tandem OLEDs. In this letter, we introduce an effective connecting structure in which an ultrathin middle metal layer is sandwiched between efficient electron- and hole-injection layers for the tandem OLEDs, which in essence, avoids the use of reactive metals during fabrication. Two-unit tandem OLEDs with such connecting structure exhibit less than double the driving voltage, yet more than double the efficiency, more saturated emission color, and longer operational lifetime compared to those of single-unit devices. A model based on a hypothesis of energy level pinning effect has been proposed as the mechanism of the connecting structure in the tandem devices. This model is also consistent with the results obtained from the photovoltaic effect measurements in tandem OLEDs.

For multicolor display applications, polymeric light emitters of the three primary colors of red, green and blue are required. Emitters of high luminescence efficiency and long lifetime stability for red and green have been found, but the search for a suitable blue emitter continues. 2,7-Disubstituted dibenzosilole monomers have been prepared by the selective translithiation of 4,4'-dibromo-2,2' diiodobiphenyl followed by silylation with dichlorodihexylsilane. Suzuki copolymerization of dibromo and bis(boronate) monomers afforded poly(9,9-dihexyl-2,7-dibenzosilole) which showed better color stability and efficiency than the corresponding polyfluorene in a single layer light emitting device. Preliminary studies demonstrated this to be a promising blue light emitting polymer.