eMagin has developed numerous enhancements to organic light emitting diode (OLED) technology, including a unique, up- emitting structure for OLED-on-silicon microdisplay devices. Recently, eMagin has fabricated full color SVGA+ resolution OLED microdisplays on silicon, with over 1.5 million color elements. The display is based on white light emission from OLED followed by LCD-type red, green and blue color filters. The color filters are patterned directly on OLED devices following suitable thin film encapsulation and the drive circuits are built directly on single crystal silicon. The resultant color OLED technology, with hits high efficiency, high brightness, and low power consumption, is ideally suited for near to the eye applications such as wearable PCS, wireless Internet applications and mobile phone, portable DVD viewers, digital cameras and other emerging applications.

The IBM Research Division and eMagin Corp. jointly have developed a low-power VGA direct view active matrix OLED display, fabricated on a crystalline silicon CMOS chip. The display is incorporated in IBM prototype wristwatch computers running the Linus operating system. IBM designed the silicon chip and eMagin developed the organic stack and performed the back-end-of line processing and packaging. Each pixel is driven by a constant current source controlled by a CMOS RAM cell, and the display receives its data from the processor memory bus. This paper describes the OLED technology and packaging, and outlines the design of the pixel and display electronics and the processor interface. Experimental results are presented.

Displays based on organic electroluminescent (EL) materials have entered the marketplace already and demonstrated remarkable contrast, high brightness and crisp colors. However, one of the key advantages of this new technology has not been commercially exploited yet: Fabrication of a display that is still fully functional even when it is bent or flexed. This is possible since organic EL devices comprising only thin, amorphous solid state films and optical properties have no critical dependence on the film thickness. In this paper we address the important elements that are required to produce a flexible organic EL display. Most crucial is the selection of a flexible substrate. Here we present results obtained with ultra-thin inorganic glass materials as well as polymeric foils. For the glass substrates we determined the ultimate mechanical properties for different device configurations. In the case of polymeric substrates permeation of water and oxygen molecules through the substrate is the governing factor. We compare the performance of different barrier systems. In summary we demonstrate that OLED devices with certain flexibility can be reliably built on ultra-thin glass substrates. For polymeric substrates a lot of progress has been achieved in terms of the required barrier properties and other necessary ingredients and this might result later into a commercial organic EL product.

In this manuscript, we report on the successful fabrication of high performance polymer light emitting diodes (PLEDs) using a low temperature, plastic lamination process. Blue- and red-emitting PLEDs were fabricated by laminating different luminescent polymers and organic compounds together to form the active media. This unique approach eliminates the issue of organic solvent compatibility with the organic layers for fabricating multi-layer PLEDs. In addition, a template activated surface process (TAS) has been successfully applied to generate an optimum interface for the low temperature lamination process. The atomic force microscopy analysis reveals a distinct difference in the surfaces created by the TAS and the spin-coating process. This observation coupled with the device data confirms the importance of the activated interface in the lamination process.

Further routes have been developed for the synthesis of a 1,4-bishalomethylbenzene derivatives for Gilch dehydrohalogenation polycondensation. Poly(2,3-dibutoxy- 1,4-phenylenevinylene) is a protoypical conjugated polymer which is thought to derive its high PL solid state fluorescence efficiency from the sterically twisted backbone and devices carrying this polymer have been further evaluated. Distyrylbenzene derivative carrying the structural feature of a 2,3-dibutoxy substitution pattern on the central ring have been prepared. One in particular has been copolymerized with a 9,9-dialkyl-fluorene-2,7- diboronate ester. The resulting conjugated polymer shows a good green emission maximum in an electroluminescent device.

In the last few years industrial research into materials fulfilling the needs of the fledgling OLED display industry have intensified considerably. At Covion we have developed a range of polymers based on phenyl-PPV derivatives which are now being commercially exploited in the first polymer LED applications. These materials have been developed systematically with the demanding requirements of the devices (e.g., high efficiency and lifetime) and the industrial applicability (e.g. processibility, reproducibility and reliability of supply) in mind. However due to market forces, such as the introduction of 3rd generation mobile communication technology, there will be an immediate demand for materials for full color OLED displays. In this paper we will report on progress in the development of Red, Green and Blue (RGB) materials at Covion. The requirements for the different colors vary depending on band gap (amongst others) and therefore the challenges for each color are different. The experience gained in understanding the important structure-property relationships in the phenyl-PPVs has been used to develop these new RGB materials.

Spin coating is a suitable technique for the fabrication of monochrome light-emitting polymer devices. For color displays, however, it is not the optimal solution when different polymers are applied. In principle, there are several technologies available for patterning light-emitting polymers. In this paper we discuss the advantages of drop-on-demand ink-jet printing over other printing methods. Special attention is given to some fundamental aspects of the printing process, such as drop formation and pixel filling. Examples of both monochrome and full color ink-jet printed passive matrix displays will be discussed.

Due to their outstanding properties organic light-emitting displays based on conjugated polymers are on the verge of commercialization. Two major disadvantages of the current processing technique for polymers, spin-coating of polymer solutions, are the material waste and the difficulties involved in patterning the polymers. Therefore we investigate the screen-printing for the production of polymer displays. Here we present performance data of screen-printed light-emitting diodes of different colors. In the production process of these diodes we printed two layers successively one over the other. Furthermore, we show images of printed multichrome demonstrators and passive matrix displays. Our data indicate that the screen-printing technique has the potential to replace the classical spin-coat process. We observe luminance of 10,000 cd/m² at 8 V and peak efficiencies exceeding 10 cd/A for green diodes and half lifetime of 170 hours at 80 degree(s)C and 100 cd/m² for red diodes which corresponds to about 7,000 hours at room temperature. These values of printed devices are comparable to those of spin-coated ones.

Investigations into the lithium fluoride and cesium fluoride/tris(quinolin-8-olato) aluminum (LiF-Alq₃ or CsF-Alq₃) Lewis acid-Lewis base pairs have been undertaken using hybrid density functional calculations. The results of the calculations clearly show that there is a strong interaction that occurs between the metal fluoride and both the facial and the meridional isomers of Alq₃. This strong interaction has the effect of modifying the electronic structure of Alq₃ and can be thought of as the first step in the formation of the highly effective Alq₃/Metal Halide/Al electron injection contact.

Efficient blue Polymer Light-Emitting Diodes (PLEDs) were fabricated by evaporating thin LiF layers between Al or Ca cathodes. Electroabsorption measurements of the built-in potential across the diodes show that devices fabricated with LiF/Ca/Al cathodes exhibit the smallest average barrier height and operating voltage (compared to both Ca and LiF/Al currently amongst the most efficient electron injectors). The turn-on bias is essentially equivalent to the built-in potential (~2.7 V), indicating an effective minimisation of the barrier to electron injection. Results are also compared with devices incorporating CsF layers and are correlated with the electroluminescent characteristics of the LEDs. A very strong dependence (~ exponential) between the built-in potential and the current and luminance at a fixed electric field (0.5MV/cm) is observed and is explained with the reduction of the cathodic barrier height brought about by the different cathode multilayers.

This paper reports on the potentialities of sol-gel deposited Sb doped SnO₂(T)) as a new transparent conducting oxide (TCO) for anode in organic light emitting diodes (OLED). Multilayered films with transparency over 85% and resistivity lower than 5 10³(Omega) -cm were obtained. Structural observations by Transmission Electron Microscopy (TEM) show that the films are nanocrystallized. Smaller and more uniform grains are obtained upon rapid thermal annealing. Atomic Force Microscopy (AFM) imaging shows the surface roughness does not exceed 20 A. TO films are very stable and cannot be chemically etched. Anode patterning by reactive ion etching (RIE) in a Methane- Hydrogen plasma has been experienced and is described. Typical etching around 250 A/min were obtained. TO/PEDOT/PVK/Al hole only diodes were realized to assess sol gel TO films as hole injection electrodes. Devices with threshold voltages of 6 volts were obtained. A comparison with ITO deposited by low temperature cathodic sputtering is given.

The electroluminescence (EL)- and electrically-detected magnetic resonance (ELDMR and EDMR, respectively) of tris- (8-hydroxyquinoline) Al (Alq₃)]/[buffer]/Al-based organic light-emitting devices (OLEDs) are described. Positive spin ½ ELDMR and EDMR observed at T<60K are similar to the typical photoluminescence-detected magnetic resonance of (pi) -conjugated polymers, and consequently attributed to enhanced polaron recombination and consequent reduction of singlet exciton quenching by trapped and free polarons. A negative spin ½ EL- and current-quenching (negative) resonance is observed at T>=60 K. Its amplitude increases with T, and it is much stronger in devices with an AlO_x buffer layer than in those with a CsF buffer. Its behavior is consistent with magnetic resonance enhancement of the spin-dependent formation of dianions at the organic/cathode interface.

Due to the 1D photonic bandgap nature of cholesteric liquid crystals, strongly circularly polarized photoluminescence can be generated by embedding fluorescent guest molecules in a cholesteric host whose resonance region coincides with the emission of the chromophores. In this paper, fluorescent guest molecules are embedded in a cholesteric reactive mesogen (RM) host, which is subsequently polymerized by UV-exposure to generate a chiral polymer. We have investigated the dependency of the form-anisotropy of the dye on the emission of circularly polarized photoluminescence by comparing highly anisotropic rod like dyes with a range of dyes of different shapes.

The measurements of the ultra-fast fluorescence anisotropy decay in conjugated dendrimers and in model branched dendritic molecules of different symmetry are reported. The excited state relaxation of carbon and adamantane-centered tetramers was investigated by polarized fluorescence upconversion spectroscopy. Fluorescence anisotropy was found to decay to the residual value in femtosecond time range. A comparison between the tetramer systems and a nitrogen cored distyrylbenzene dendrimer is provided. For the model system bis-MSB representing the linear building block of the investigated systems a fluorescence anisotropy decay time of 82 ps was obtained which agrees with rotational diffusion. Ultrafast anisotropy decay for these branched systems was explained in terms of interchromophore interactions. The results of these ultrafast anisotropy measurements are important to the understanding of the characteristics of excitations in organic dendrimers.

Charge based deep level transient spectroscopy (Q-DLTS) has been used to investigate the defect states of poly (p phenylene vinylene)(PPV) light emitting diodes. Studies in the temperature range 250-315K show the presence of two carrier trapping centers in the polymer bulk: a majority carrier trap at 0.5 eV with a cross section of 10^-16cm² and a minority carrier trap at 0.4eV with a cross section of 10^-19cm². The results are compared and discussed with those previously reported in PPV based diodes using other techniques to determine the trap parameters in the polymer.

The paper describes the use of noise current analysis to sense variations of the microscopic conduction process in organic Light Emitting Diodes and to track their evolution through time. The monitoring of current fluctuations has been made both in time and frequency domain and is of great value when one wants to correlate the conduction properties of the charge carriers and the changes in current flow with the corresponding changes in the microscopic morphology of the organic layers. The method reveals itself to be very effective also in sensing the initial state and the growth of catastrophic degradation of oLEDs in large advance with respect to current monitoring or other techniques. Microscopic damages within the device, as a result of microshorts and/or thermal breakdown, are shown to reveal a neat increase of the white noise component of about three orders of magnitude in the power spectral density, that can therefore be detected with very good time precision. This would allow to study the sources that may give reason of degradation, through structural or spectroscopic investigations for example, before the microscopic damages have sum up to a visible and irreversible macroscopic failure.

Using a combination of ultraviolet and x-ray photoelectron spectroscopies (UPS, XPS), we have studied the relative energy level alignment of two phosphorescent guest molecules, 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine platinum (PtOEP) and tris(2-phenylpyridine)iridium (Ir(ppy)3), doped in an electron transport host, tris(8-hydroxyquinolinato) aluminum (III) (Alq3), and in a hole transport host, 4,4'-bis(carbazol-9-yl)biphenyl (CBP). In each of the guest-host systems, we find that the vacuum levels of the guest and the host molecules align, and that the position of the highest occupied molecular orbital (HOMO) of the phosphorescent guest is independent of the guest molecule concentration (0.8 - 56% by mass) in the composite films. These results are used to shed light on possible electroluminescence mechanism(s) in the emissive layer of an organic light-emitting device utilizing the studied guest-host structures.

Quinoxaline model compounds are interesting materials for Organic Light Emitting Devices (OLEDs) because of their thermal stability and their higher ionization potential in comparison to other electron transporting/hole blocking materials. In this work we studied a starburst trisphenylquinoxaline by means of Ultraviolet Photoelectron Spectroscopy (UPS) and Thermally Stimulated Luminescence (TSL). UPS provided not only the characterization of the valence band structure but also parameters like ionization potential, 6 eV, and, combined with absorption spectroscopy, electron affinity, that are of crucial importance in designing optimized OLED configurations. On the other hand, a wide distribution of localized states occurs in organic layers due to several factors and TSL can investigate these states. The combination of the used techniques together with semi-empirical quantum chemical calculation, gave a detailed description not only of the valence and conduction band of the studied materials, i.e. the energy position of HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital), but also of the trap distributions localized in the band gap: a shallow one at 0.06 eV and a deeper state centered at 0.24 eV. The full spectroscopic and electrical characterization of the material formed the background for understanding its behavior in heterolayer devices.

We report a photoemission study of the interfaces between spin-cast films of a new variation of a polymer blend consisting of poly(3,4-ethylenedioxy-thiophene) (PEDOT) and poly(4-styrenesulfonate) (PSS) and glycerol as an additive, and vacuum-evaporated hole transport layers (HTL) of 4,4'-bis(carbazol-9-yl)biphenyl (CBP),N,N'-diphenyl-N,N'-bis(1-naphthyl)-1-1'biphenyl-4,4'di amine (NPD) and N,N'-diphenyl-N,N'-bis(3methylphenyl)-1,1'-biphenyl-4,4'-dia mine (TPD). The hole injection barrier, as deduced from photoemission spectroscopy, is 0.5 - 0.9 eV at the PEDOT-PSS / HTL interface, which compares very well with the previously reported barrier heights for oxygen plasma -treated indium-tin oxide (ITO)/NPD and ITO/TPD interfaces, and which is, most notably, a factor of two smaller than barriers measured for a PEDOT-PSS/hole-transporting luminescent polymer, e.g. poly(bis-(2-dimethyloctylsilyl)-1,4-phenylvinylene, interface. The measured energy barriers imply a sufficiently efficient charge injection at the studied PEDOT-PSS/HTL interface, which is very encouraging for further development of anode structures based on similar conducting polymer blends and chemically modified structures to be utilized in molecular organic light-emitting device applications.

In order to get a detailed understanding of organic light-emitting devices (OLEDs), optimize their performance and provide reliable data for device modeling, we have developed an ultra-high vacuum (UHV) evaporation system for combinatorial studies. Our system allows the simultaneous fabrication of 10 x 10 individual devices on one substrate enabling a systematic variation of material combinations and electrodes as well as device parameters such as layer thickness, layer sequence, dye dopant concentrations. Here, we present an overview of the capabilities of combinatorial methods for electrical and electro-optical device optimization. We show results on multilayer OLEDs ranging from the conventional copper-phthalocyanine (CuPc)/N,N'-di(naphtalene-1-yl)-N,N'-diphenyl-benzidine (NPB)/ and tris-(8-hydroxyquinolinato)aluminum (Alq) trilayer device to double-doped, red-emitting OLEDs with efficiencies up to 1.5 cd/A at 20 mA/cm² measured through a semitransparent metal electrode and CIE color coordinates of x=0.65, y=0.34.

The emission of light and the external coupling after the appropriate excitons have been formed in the organic light-emitting devices has been investigated. A combined classical and quantum mechanical model was used to calculate the distribution of the internally emitted light into the externally emitted and various waveguided modes in an organic light-emitting device on planar substrates. The exciton lifetime in the OLED cavity was calculated by a Green's function formalism, with a focus on the non-radiative energy transfer to the cathode. Various efficiency measures as a function of the thickness of the indium-tin-oxide anode were calculated and the numerical results were in agreement with the measured external quantum efficiencies.

A novel class of amorphous molecular materials, 1,3,5- tris(4-biphenylyl)benzene (TBB), 1.3.5-tris(4- fluorobiphenyl-4'-yl)benzene(F-TBB), 1,3,5-tris(9,9- dimethylfluoren-2-yl)benzene(TFB), and 1,3,5-tris[4-(9,9- dimethylfluoren-2-yl)phenyl]benzene(TFPB), were found to function as hole-blocking materials in organic electroluminescent (EL) devices. 1.3.5-Tris[5- (dimesitylboryl)thiophen-2-yl]benzene(TMB-TB) was also found to function as an electron transporter with better hole- blocking properties relative to tris(8- quinolinolato)aluminum. These materials, which readily form stable amorphous glasses with well-defined glass-transition temperatures, are characterized by relatively high oxidation potentials and large HOMO-LUMO energy gaps. The use of these materials as hole blockers in multilayer organic EL devices permitted efficient blue-violet emission from emitters with hole transporting properties, e.g., N,N'bis(e- methylphenyl)-N,N'-diphenyl-[1,1'-biphenyl]-4,4'-diamine (TPD), N,N'-bis(4-biphenylyl)-N,N'-diphenyl-[1,1'-biphenyl]- 4,4'-diamine(p-BPD), N,N-bis(9,9-dimethylfluorene-2- yl)aniline (F₂PA), N,N'-bis[9,9-dimethylfluoren-2-yl]- N,N'-diphenyl-9,9-dimethylfluorene-2,7-diamine (PFFA), and N,N,N',N'-tetrakis(9,9-dimethylfluoren-2-yl)-[1,1'- biphenyl]-4,4'-diamine(FFD).

Poly(9,9-dicotylfluorene)(PFO) exhibits very good, non- dispersive hole transport but very poor electron transport. To achieve the maximum efficiency in a PFO light emitting diode it is important to balance the electron and hole currents. Here we report three schemes to achieve this in single layer devices. Firstly, by using different treatments to change the work function of the indium tin oxide anode contact, the hole current can be varied by up to 4 orders of magnitude, thus allowing it to be adjusted to the same level as the electron current. Secondly, the hole mobility can be decreased by doping PFO with a hole trapping, emissive material. Upon the addition of 5% by weight of a red-emitting tetraphenylporphyrin, hole transport in PFO becomes as highly dispersive as electron transport, resulting in a decrease in the current for a given applied bias but an increase in the electroluminescent efficiency. Thirdly, the electron mobility can be increased by doping PFO with an emissive, electron transporting material. The electroluminescent polyfluorene copolymer poly(9,9-dioctylfluorene-co-benzothiadiazole (BT) exhibits strong but dispersive electron transport. PFO devices doped with BT show very high efficiencies, high peak brightnesses and very low turn on voltages.

In the framework of trap-free steady-state space-charge-limited single-carrier currents, exact equations are derived for the evaluation of arbitrary field-dependent mobility. A differential method, which simply needs first and second derivatives of measured current-voltage (I-V) curves, is put forward. No a priori assumptions are required, other than those which are typical for space-charge-limited currents. An extension to the mixed case of exponentially distributed traps and field-dependent mobility is briefly outlined. The extraction of mobility from measurements can be a valuable tool for the theoretician: theoretical predictions on mobility field-dependence can be easily compared to the real field-dependence, thus permitting an improvement of the model and stimulating the development of transport theory. This method can be of particular relevance for organic semiconductors, whose field-dependent mobility has recently attracted so much theoretical and experimental work.

The electronic structure of poly(9,9-dioctylfluorene)(PFO) in different molecular weights coated with alkali metals (K and Cs) has been studied by x-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). No significant differences on the electronic structures were observed for all combinations of alkali metals and PFO in different molecular weights. These metals led to low injection barrier at the K/PFO or Cs/PFO interfaces and induced bipolaron gap states in the PFO. With increasing coverage of the alkali metals, the bipolaron states and the highest-occupied molecular orbitals gradually broadened, and the two shake-up peaks of Cls XPS peaks associated with the lowest-unoccupied molecular orbitals of PFO also broadened and greatly diminished. Upon slight oxygen exposure, the two bipolaron states disappeared and the deformed features in the UPS and XPS spectra were partially recovered.

We have studied the effects of using a composite fabricated from carbon nanotubes and a host polymer, poly(m-phenylene-vinylene-co-2,5-dioctyloxy-p-phenylene-viny lene) (PmPV), as an electron-transport layer in organic light-emitting diodes. Double layer devices using this composite as an electron-transport layer, triple layer devices with a composite electron-transport layer and poly(9-vinylcarbazole) (PVK) as a hole-transport layer, as well as poly(2,5-dimethoxy-1,4-phenylene-vinylene-2-methoxy-5(2'-eth ylhexyloxy)-1,4-phenylene-vinylene (M3EH-PPV) single layer devices were prepared. Current-voltage-luminance and electroluminescent spectral measurements were performed using six different nanotube powder to polymer mass ratios (0, 2, 4, 8, 16, and 32%) for all device structures studied. DC transport and photoluminescence behavior of the polymer-nanotube composite were also investigated. Although a potential barrier is introduced at the M3EH-PPV/composite interface, a significant increase in efficiency was observed using the composite. The best efficiency was obtained for those devices with an electron-transport layer of mass ratio 8%. In addition, on doping with nanotubes, electron conductivity in the composite increased by over four orders of magnitude with little quenching of photoluminescence.

Several class of dyes doped in deoxyribonucleic acid (DNA) derived from salmon show enhancement of fluorescence due to suppression of molecular aggregation. Also, some recent studies support electric conduction in DNA strands. Combination of these properties suggests the possibility to develop organic LED devices (OLED) based on biopolymer systems. Furthermore, the electroluminescence (EL) effect can be employed as a probe for electrical and optical properties of DNA. We fabricated OLED devices based on DNA- lipid complex and dopant dyes (ethidium bromide and fluorescein). Devices are composed of hole injection layer, dye-doped DNA-lipid layer and electrodues. OLED with ethidium bromide doped DNA showed LED emission under DC bias, but the origin of the emission was tris-(8- hydroxyquinolinato)aluminum(III)(Alq3) which was employed as an electron transporter. The current-voltage characteristics of the devices show apparent rectification behavior. From these experimental results, it is confirmed that DNA transports hole current under external DC bias. When employing fluorescein as a dopant in DNA and fabricating the devices without Alq3 layer, we observed emission from the dyes incorporated in DNA. Although the origins of the emission centers in spectra are not clear, it shows that the DNA-lipid complex will be basically applicable to OLED if additional improvements are made.

We derive a macroscopic drift-diffusion equation for charge carrier mobilities in disordered materials. Our procedure takes site blocking and internal field effects explicitly into consideration. The final expression contains several drift terms originating from spatial inhomogeneities and energetic disorder. Thus even a spatial variation of the hopping rates is allowed, if local detailed balance still holds. The main advantage of our approach is a time-dependent numerical solution of the drift-diffusion equation for all positions within a sample without resort to a lattice description or a finite element analysis. We discuss our numerical results for important cases of spatial disorder and energy density of states within a sample and follow the space-time evolution of local charge distributions. The occurrence of shock waves is discussed both theoretically by giving asymptotic solutions and in simulations.

Tetraphenylsilane derivatives attached with one to four of N,N-diphenylaninooxadiazole(TPAOXD) blue fluorescent moieties, namely Si(PhTPAOXD)₄, PhSi(PhTPAOXD)₃, PH₂Si(PhTPAOXD)₂, and Ph₃Si(PhTPAOXD), were synthesized and characterized. Tetraphenylsilane core structure provides an effective molecular skeleton for inhibiting the crystallization of the material. Very bright blue electroluminescence (>20,000 cd/m²) was observed for a trilayer device with configuration of ITO/NPB/PH₃Si)PhTPAOXD)/Alq₃/Mg:Ag. The electroluminescence of the device, in terms of emission wavelength and chromaticity, is highly dependent on the thickness of emitting layer. The current-voltage-electroluminescence characteristics of the devices are described.

Various surface treatments significantly affect the work function and surface roughness of indium tin oxide (ITO), and thusly influence charge injection and overall performance of organic light emitting diodes (OLEDs). Large number of treatments, most commonly oxygen plasma treatment and UV-ozone treatment, have been proposed to improve characteristics of ITO. In this work, we have investigated a)mechanical treatments (mechanical rubbing, followed by ultrasonic bath), b)chemical treatments (dipping into aqueous solutions of various acids, including acids which have not been investigated previously) c)thermal treatments (thermal annealing in different atmospheres) d) plasma treatments e) UV ozone treatment f) different combinations of the above. We have measured surface sheet resistance of the samples and investigated surface morphology of the treated samples and compared them to as-received samples. We have selected several treatments giving best results. Then we have fabricated OLEDs using ITO substrates treated with treatments selected, as well as a control OLED fabricated on as-received ITO. The impact of ITO treatments on the performance of OLEDs have been investigated on two types of devices, OLEDs with and without transport layer, having the structures glass/ITO/Alq₃/Al and glass/ITO/TPD/Alq₃/Al, respectively, where Alq₃(tris-(8-hydroxyquinoline)aluminum) is emitting layer and TPD(N,N'-diphenyl-N,N'-bis(3-methyl-phenyl)-1,1'biphenil- 4,4'diamine) is a hole transport layer.

A series of 9,9-bis(diarylaminophenyl)fluorene derivatives (X-APFs) were synthesized and used as hole-transporting materials in single hetero-junction light-emitting device fabrication. In devices with tris(8-hydroxyquinoline) aluminum (Alq) as the electron-transporting material, these materials served the role of hole-transporters only. The device performance (turn-on voltage, luminance efficiency and etc) shows a dependence on the substituent on the phenyl ring. In devices with 2,2'2'-(1,3,5-phenylene)tris-[1- phenyl-1H-benzimidazole](TPBI) as the electron-transporting material, a complex electroluminescence behavior was observed, depending on the substituent as well as the applied voltage. The results are discussed in terms of energy level matching and the effect of electric field on the molecular geometry.

Bipolar p-TPAOXD and m-TPAOXD are both tetraphenylmethane- based isomeric compounds containing triphenylamine- substituted 1,3,4-oxadizaole moieties. Two are amorphous materials showing no melting or crystallization transition but only glass transition at 187 and 149 degree(s)C, respectively. Single-layer organic light-emitting devices based on p-TPAOXD or m-TPAOXD as active layer were fabricated via spin-casting method. With varied fabrication conditions (solvent, cathode material, and film thickness) devices with turn-on voltage as low as 4V, blue electroluminance with intensity of 1,700 cd/m², and photometric efficiency larger than 0.7 cd/A can be achieved for p-TPAOXD. The luminance and photometric efficiency of the device containing m-TPAOXD are low (always less than 100 cd/m² and 0.2 cd/A) as compared to those containing p- TPAOXD.

Some novel 2, 5, 9, 12- tetra-substituted quinacridones were synthesized. The comparison of absorption spectra and fluorescence spectra of these soluble quinacridones between in solutions and in solid film indicated that the formation of intermolecular hydrogen bonds in the crystalline was obstructed by N-alkylation. These compounds have good solubility in common solvents such as dichloromethane, chloroform, acetone, DMF etc. The good solubility provides an opportunity for a higher doping concentration of the quinacridone fluorophore chromophore in the application of photoelectronic devices. The longer fluorescence lifetimes (ca. 20 ns) of these soluble quinacridones were measured by single-photon counting technique, which seems to be hopeful for the luminescence application. The EL device made with the soluble quinacridone show a luminance of 150 cd/m² and injected current as high as 400 mA/ cm² at 18 V.

Amorphous carbazole derivatives containing peripheral diarylamines at the 3- and 6-positions and an ethyl or aryl substituent at the 9-position of the carbazole moiety have been synthesized. These new carbazole compounds (carbs) possess high glass transition temperatures (T_g: 120- 194 degree(s)C) and high thermal decomposition temperatures (T_d>450 degree(s)C). The compounds are weakly to moderately luminescent with the emission wavelength ranging from green to blue. Two types of light-emitting diodes (LED) were constructed from carb:(I)ITO/carb/TPBI/Mg:Ag and (II)ITO/carb/Alq₃/Mg:Ag, where TPBI and Alq₃ are 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene and tris(8- hydroxyquinoline) aluminum, respectively. In type I devices the carb functions as the hole-transporting as well as emitting material. In type II devices either carb and/or Alq₃ is the light emitting material. Several green light-emitting devices exhibit exceptional maximum brightness and the physical performance is superior to those of typical green-light-emitting devices of the structure ITO/diamine/Alq₃/Mg:Ag. Relation between the LUMO of the carb and the performance of the light-emitting diode is discussed.

Using the methodology of traveling-wave lasing in neat films (amplified spontaneous emission, ASE) we have investigated the novel polycondensation-type MEH-PPV 1(strictly linear and fully conjugated) and some of its alternating copolymer combinations with 2,5-dialkoxy-phenylenevinylene (2-5) and thianthrene-vinylene (6-8) units. Well-defined, solution- processable, high-molecular weight samples (Mw = 20.000 - 60.000) have been prepared via the polycondensation route employing the repetitive HORNER carbonyl-olefination. This is based on the reaction of appropriate xylylene bis(phosphonates) with dialkoxy-substituted phenylene dialdehydes and dibenzoyl-thianthrene (dibenzoyl-benzene), respectively. In previous studies Thianthrene-PPVs were reported to display green EL from single layer devices while the dialkoxy-PPVs are known to display orange or red EL. Here, traveling-wave lasing studies are performed on neat films. Solution cast amorphous film samples on glass substrates are transversally pumped with picosecond laser pulses (wavelength 347 nm, duration 35 ps). Lasing occurs at 622 nm for MEH-PPV 1, 646 nm (M3EH-PPV 2), 629 nm (MEH- DOO-PPV 3), 629 nm (DMO-DO18-PPV 4), 522 nm (Thianthrene- MEH-PPV 7) and at 647 nm and 630 nm for the new M3EH-OPV containing terpolymers (DP-MEH-OPV)_0,25n(M3EH-OPV)_0,75n5 and (Thianthrene-MEH-OPV)_o,5n(M3EH-OPV(_0,5n8, respectively. The spectral widths of emission are less than 13 nm. Laser threshold energy densities are found to be rather low, ranging between 4 and 18(mu) jcm^-2. The effective lengths of amplification are roughly 1 mm. These results show that all the condensation polymers under investigation are good solid-state laser materials for optically pumped disk, ring and DFB lasers and that they are potential candidates for electrically pumped lasers. Furthermore, it is demonstrated that amorphous blends of the polycondensation-type MEH-PPV 1 with the electroactive DPOP- PPV (ratio 50:50, 30:70 p. wt.) Or Thianthrene-MEH-PPV 7 (ratio 50:50, 22:78 and 5.6:94.4 p. wt.) exhibit red ASE around 590 - 615 nm as the result of energy (exciton) transfer from the green emitting donor materials to the MEH- PPV acceptors.

Organic polymer red light-emitting devices (OPLEDs) with the double layer structure have been fabricated on flexible plastic substrates. Dow red emissive polymer and poly(3,4- ethylenedioxythiophene)/poly(styrene)(PEDOT/PSS) have been used as an emissive and a hole injection polymer, respectively. The spin coating technique was used to deposit different polymers. The absorption and the cyclic voltammetry spectra have been used to construct the band diagram of our OPLEDs. The following electrical and optical properties have been obtained for our OPLEDs: turn-on voltage, defined at 1 cd/m²=~3.0V; voltage and current density defined at 100 cd/m²=~6.5V and ~34mA/cm²; maximum emission efficiency =~0.25 cd/A; and maximum luminous efficiency =~0.1m/W. The extrapolated lifetime of unpackaged OPLEDs on flexible plastic substrate of about 1160 min for initial brightness of 100 cd/m² has been obtained.

Bright [indium tin oxide (ITO)]/[N,N'-diphenyl-N,N'-bis(1- naphthyl-phenyl)-1,1'-biphenyl-4,4'-diamine(NPB)]/[2 wt.% perylene-doped 4,4'-bis(9-carbazolyl) biphenyl (CBP)]/[2-(4- biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (Bu- PBD)]/[2 wt.% 4-(dicyano-methylene)-2-methyl-6-(p-dimethyl aminostyryl)-4H-pyran (DCM1)-doped tris-(8-hydroxy quinoline) Al(Alq₃)]/CsF/Al OLEDS are described. The electroluminescence (EL) spectra consist of blue and green bands at 453, 487, and 524 nm due to perylene and a red band at 600 nm due to DCM1, i.e., the emission zones are completely separated by the Bu-PBD. As the thickness of the NPB and perylene: CBP layers increases and that of the DCM1:alq₃ layer decreases the intensity of the perylene emission increases strongly relative to the DCM1 emission. For 350 A thick NPB, 350 A thick perylene: CBP, 100 A Bu- PBD, and 150 A DCM1:Alq₃, the onset voltage is 6.5 V, the brightness reaches 3750 Cd/m² at 20 V, the efficiency is 2.4 Cd/A at 19V, and the (x,y) CIE coordinates are well within the white region. However, as the bias is increased the intensity of the perylene emission increases relative to the DCM1 emission, so (x,y) evolves from (0.42, 0.35) at 14V to (0.29, 0.32) at 21V. Both the layer thickness- and bias-dependence are believed to result from changes in the recombination zone and in the field-and cathode-mirror- induced quenching of the DCM1 singlet excitons.

Brightness and color resolution, wider viewing angles, lower power consumption, and a thin aspect ratio are all well understood physical characteristics of organic light emitting diode (OLED) displays, an up-and-coming flat panel displays. Increasing numbers of applications of flat panel displays are being commercialized with touch screens. This paper will describe the optical characteristics of mating a touch screen with a full-color active matrix OLED display. We will quantify the OLED optical properties with respect to touch screens with matte finishes and anti-reflective topcoats, and with and without the use of a polarizer on the OLEDs top glass.

Transparent conducting indium tin oxide (ITO) tin films were grown by pulsed-laser deposition (PLD) on glass and single crystal yttria-stabilized zirconia (YSZ) substrates. The structural, electrical and optical properties of these films were investigated as a function of substrate deposition temperature and background gas pressure. Films were deposited using a KrF excimer laser (248nm, 30 ns FWHM) at a fluence of 1.2 J/cm². Films were deposited at substrate temperature of 300 degree(s)C in mixed gases (12 mTorr of argon and 1-50 mTorr of oxygen). X-ray diffraction, scanning electron microscopy and atomic force microscopy were used to characterize the structure and morphology of the deposited films. UV/VIS/NIR spectroscopy and Hall effect measurements were used to characterize the optical and electrical properties of the films. ITO films (300 nm thick), deposited by PLD on YSZ at 300 degree(s)C in a gas mixture of 12 mTorr of argon and 5 mTorr of oxygen, exhibit a low electrical resistivity (1.6 x 10^-4(Omega) -cm) with a high transparency (~74%) at 550 nm. ITO films deposited by PLD on both glass and YSZ substrates have been used as an anode contact in organic light-emitting diodes. A comparison of the device performance for the two substrates shows that the device fabricated on the ITO/YSZ has a higher external quantum efficiency than that of the device fabricated on the ITO/glass.

Organic thin-film transistors (TFTs) using the pentacene as an active electronic material have shown the mobility of 0.8 cm²Vs and the grains larger than 1 micrometers . Deep level transient spectroscopy (DLTS) measurements have been carried out on metal/insulator/organic-semiconductor (MIS) structure devices that have a depletion region at the insulator/organic-semiconductor interface. The very long capacitance transients were measured by the trapping of electronic charge carriers distributed in energy. Based on the DLTS characteristics, the energy levels of hole and electron traps in the obtained pentacene films were approximately E_v+0.24eV, E_v+0.31eV, and E_c- 0.69eV.

A series of naphthalimides containing schiff base moiety were prepared by condensation of 4-hydrazino-1,8-naphtahlimides with subsititued formaldehyde. Electronic interaction between the 4-amino-1,8-naphthalimide and the substitutent moiety results in red shift of the absorption and fluorescence maximum wavelengths in the acetonitrile solution and in the solid state. Some of these dyes emit brilliant red fluorescence in the solid state.

Organic light emitting diodes generally suffer from higher operating voltages compared to inorganic ones. This limits their application in passive or active driven displays based on OLED-technology. As was previously shown by our group, p-type doping of the hole injection and transport layer of an organic light emitting diode (OLED) by co-evaporation of a matrix and an acceptor molecule leads to lower operating voltages of the device. In OLEDs using doped transport layers, the use of a proper buffer layer between the doped layer and the light emission layer is essential to yield a high current efficiency and a low operating voltage at the same time. In order to further enhance the device efficiency, we apply here the doping concept to OLEDs with a light emission layer which is doped with a fluorescent dye. This approach proves that doping of the transport layer is able to improve the optoelectronic properties of already highly efficient OLEDs. The doped hole injection and hole transport layer is a Starburst layer p-type-doped with tetrafluoro-tetracyano-quinodimethane (F₄-TCNQ). As blocking layer, a diamine (TPD) is used. The emitter layer consists of quinacridone (QAD) doped aluminum-tris-(8-hydroxy-quinolate) (Alq₃). Holes are injected from untreated ITO, electrons via a lithium-fluoride (LiF)/aluminum cathode combination. For this OLED layer sequence, we achieved a luminance of 100cd/m² in forward direction at the lowest operating voltage reported for completely non-polymeric OLEDs (3.2-3.4V) with a current efficiency of around 10cd/A.

Arrays of UV-violet [indium tin oxide (ITO)]/[copper phthalocyanine (CuPc)]/[4,4'-bis(9- carbazolyl)biphenyl(CBP)]/[2-(4-biphenylyl)-5-(4-tert- butylphenyl)-1,3,4-oxadiazole(Bu-PBD)]/CsF/Al organic light- emitting devices (OLEDs), fabricated combinatorially using a sliding shutter technique, are described. Comparison of the electroluminescence spectrum with the photoluminescence spectrum of CBP indicates that the emission originates from the bulk of that layer. However, due to the high gap of CBP and the strong hole capture cross section of perylene contaminants, it was difficult to completely eliminate the emission from the latter. In arrays of devices in which the thickness of the CuPc and Bu-PBD were varied, but that of CBP was fixed at 50 nm, the optimal radiance R was obtained at CuPc and Bu-PBD thicknesses of 15 and 18 nm, respectively. At 10 mA/Cm², R was 0.38 mW/cm², i.e., the external quantum efficiency was 1.25%; R increased to ~1.2 mW/cm² at 100 mA/cm².

Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) aqueous dispersion (PEDOT:PSS) is a highly conductive polymer. Attempts to utilize them as an anode in an organic light emitting diode have been made but a satisfactory result was not obtained due to low device efficiency caused by the relatively high surface resistance and poor optical transparency. We recently reported that the conductivity of the PEDOT:PSS (Baytron P by Bayer) was dramatically increased without losing the optical transparency by addition of a small amount of a polyalcohol. Here, we present the improved I-V-L characteristics of the molecular organic light emitting diodes fabricated using the highly conductive and transparent PEDOT:PSS as an anode.

Phenyl, ethynyl-silyl and ethynyl-alkyl derivatives of pentacene have been optically characterized and their use as potential red emitters in organic light emitting devices is investigated. Tuning of the red emission wavelength and photoluminescence quantum efficiency ((phi) pl) is achieved by modifying the substituent and its position on the pentacene backbone. A red shift in the emission maxima ((lambda) max) is observed upon addition of more phenyl groups or changing from a phenyl to an ethynyl-R due to an increase in (pi) -conjugation. For example, the (lambda) max of 6,13-diphenylpentacene (DPP) is 617nm compared to 630nm for 5,7,12,14-tetraphenylpentacene (TPP). Similarly, the diethynyl pentacene derivatives have a red shifted (lambda) max (638nm), relative to that of DPP, due to the greater conjugation associated with the triple bond of the ethynyl group. DPP is explored as a red emitter in a universal blue host due to its ideal red chromaticity and good (phi) pl. Red and green emission is achieved in multi-layered devices through the incorporation of an emitting layer based on a blue-emitting/electron transporting universal host, 5,5'-bis(dimesitylboryl)-2,2'-bithiophene (BMB-2T), doped with fluorescent red and green emitters, respectively. Blue emission can be obtained from the host BMB-2T, or from the adjacent hole transporter. A hole-blocking layer is used for the latter case to force electron and hole recombination in the hole transporting layer. The host and guest molecules are selected in order to take advantage of two electroluminescence mechanisms, energy transfer from host to guest and direct carrier recombination on the guest molecules. Hence, one can tune the emission color while maintaining high device efficiency. This approach is also technologically advantageous because it minimizes the number of materials used, reduces cross contamination and production costs.