This PDF file contains the front matter associated with SPIE Proceedings Volume 7415, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

We studied changes in photoluminescence yield of 9,10-bis (2-naphthyl)-2-t-butylanthracene (TBADN), a commonly used blue emitter in organic light emitting devices (OLEDs). Our studies show that, unlike in case of tris (8-hydroxyquinoline) aluminum (AlQ₃), current flow does not bring about a significant change in TBADN photoluminescence yield under 400nm excitation. We attribute the different behavior of TBADN to its bipolar carrier transport nature, which, in comparison to AlQ₃, does not facilitate the build-up of significant space charges. Excitation at 360nm, however, leads to a rapid decrease in photoluminescence yield, even in the absence of electrical stressing, revealing that higher excited states of TBADN are less stable, and suggesting they could be playing a role in OLED electroluminescence degradation.

We have developed an apparatus (Hamamatsu C9920-02) for measuring the absolute photoluminescence quantum yield. This system consists of an excitation light source, a sample holder mounted in an integrating sphere and a multi-channel CCD spectrometer. Using this apparatus, the absolute phosphorescence quantum yields were measured for several iridium complexes doped in organic thin films or dissolved in deaerated solutions. The iridium complexes fac-tris (2-phenylpyridine)iridium(III) (Ir(ppy)₃) and its derivatives, showed high phosphorescence quantum yields (>90 %), while bis(2-(2'-benzo(4,5-a)thienyl)pyridinato-N,C^3')iridium(III)(acetylacetonate) (Btp₂Ir(acac)) gave a lower phosphorescence quantum yield (less than 40 %). To reveal the mechanism of nonradiative decay of the excited iridium complexes, we made time-resolved photoacoustic measurements. It was found that all of the iridium complexes undergo S₁-T₁ intersystem crossing with efficiencies of close to 100 % after photoexcitation. This indicates that the lower phosphorescence quantum yield for Btp₂Ir(acac) is due to involvement of the T₁-S₀ intersystem crossing process.

Conductivity doping of charge transporting layers is becoming increasingly attractive for improving power efficiency in OLEDs. However, the number of commercially available organic molecular p-dopants is limited. The electron acceptor 2,3,5,6-tetrafluoro-7,7,8,8,-tetracyanoquinodimethane (F4-TCNQ) is the most utilized p-dopant. F4-TCNQ can be used as a dopant for most hole transporting materials (HTM), but it is very volatile, which makes it difficult for vacuum processing, and has a low sticking coefficient. Here we present the design of novel anchored molecular dopants based on the TCNQ core. We first review how the reduction potential of TCNQ core is affected by substitution with alkyl groups of different electronic properties. Electron donating groups have negative effect on the reduction potential of the acceptor. However, attaching electron withdrawing groups such as halogens counteracts the effect of electron donating groups. Using gas phase theoretical calculations we determined that trifluorinated TCNQ can be anchored through a σ-coupled alkyl chain to an inert molecular anchor without sacrificing the electron affinity.

Highly efficient light-emitting materials based on phenylquinoline-carbazole derivative has been synthesized for organic-light emitting diodes (OLEDs). The materials form high quality amorphous thin films by thermal evaporation and the energy levels can be easily adjusted by the introduction of different electron donating and electron withdrawing groups on carbazoylphenylquinoline. Non-doped deep-blue OLEDs using Et-CVz-PhQ as the emitter show bright emission (CIE coordinates, x=0.156, y=0.093) with an external quantum efficiency of 2.45 %. Furthermore, the material works as an excellent host material for BCzVBi to get high-performance OLEDs with excellent deep-blue CIE coordinates (x=0.155, y=0.157), high power efficiency (5.98 lm/W), and high external quantum efficiency (5.22 %). Cyclometalated Ir(III) μ-chloride bridged dimers were synthesized by iridium trichloride hydrate with an excess of our developed deep-blue emitter, Et-CVz-PhQ. The Ir(III) complexes were prepared by the dimers with the corresponding ancillary ligands. The chloride bridged diiridium complexes can be easily converted to mononuclear Ir(III) complexes by replacing the two bridging chlorides with bidentate monoanionic ancillary ligands. Among the various types of ancillary ligands, we firstly used picolinic acid N-oxide, including picolinic acid and acetylacetone as an ancillary ligands for Ir(III) complexes. The PhOLEDs also shows reasonably high brightness and good luminance efficiency of 20,000 cd/m² and 12 cd/A, respectively.

In this manuscript, non-classical nonvertical triplet acceptors are proposed as a promising class of efficient triplet scavengers for future solid-state electrically pumped organic lasers. Triplet excitation scavenging is investigated in polymer films of polyfluorene, a prospective material for the fabrication of thin-film organic lasers. Two dopant molecules, cyclooctatetraene (COT, a nonvertical triplet acceptor) and anthracene (a vertical triplet acceptor), are studied and the occurrence of anomalous nonvertical triplet energy transfer in solid conjugated polymer films is demonstrated for the first time employing COT.

Host materials for phosphorescence organic light-emitting diodes (OLEDs) are required to have wide energy gap to prevent back energy transfer and confine triplet exciton on guest molecules. Carbazole (Cz) has been widely used as a building block for host materials because of its relatively high energy gap. We found that the energy gap of Cz can be widened by fluorination at specific positions. A characteristic of the energy gap widening by fluorination is its controllability by the number and position of fluorine substituents. We synthesized 2,7-difluorocarbazole (F-Cz) and estimated the energy gap of Cz and F-Cz from absorption spectra to be 3.59 eV and 3.71 eV, respectively. To confirm the wide-gap effect of F-Cz on OLED device, we synthesized a solution-processable polymer host, poly(N-vinyl-2,7-difluorocarbazole) (F-PVK), which has F-Cz as pendant groups, and compared it with poly(N-vinylcarbazole) (PVK). The OLED devices investigated consisted of an ITO/PEDOT:PSS/EML/CsF/Al multilayered structure. The poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) layer was spin-coated onto an indium tin oxide (ITO) coated glass substrate. Subsequently, the emission layer (EML) composed of PVK or F-PVK, 1,3-bis[(4-tertbutylphenyl)-1,3,4-oxidiazolyl]phenylene (OXD-7), and a blue phosphorescent dopant, iridium(III)bis [(4,6-difluorophenyl)-pyridinato-N,C2'] picolinate (FIrpic) was spin-coated, and the CsF and Al layers were vapor-deposited. The OLED device with F-PVK showed 1.8 times higher maximum current efficiency (27 cd/A) than that with PVK (15 cd/A). The improved efficiency of F-PVK device can be rationalized by the enhanced triplet confinement effect of polymer host composed of fluorinated carbazole.

Electro-modulation (EM) is used to measure interfacial hole densities in operating OLEDs. This in-situ optical probe has provided us with a measure of relative hole and electron currents in a wide range of OLED structures. Insight to the dynamics of interfacial hole densities allows an assessment of the longterm stability of electron-hole balance, and therefore helps greatly with the identification of electroluminescence (EL) degradation mechanisms. Here, we limit the investigation to NPB/AlQ3 OLEDs, but note that the technique is versatile, and can be readily adapted to a wide range OLED structures, especially those comprising arylamine -based hole transport materials and interlayers.

Theoretical equations for current-voltage characteristics in mono-layer unipolar devices and multilayer bipolar device (that is, OLED) are investigated on the basis of the model consisting of diffusion theory of internal carrier emission through Schottky barrier at cathode and anode electrodes and electronic field dependence of carrier mobility, so called Pool-Frenkel mobility. Space charge effects are also included in this model, which is not presented as a simple Mott- Gurney law. The current-voltage characteristics of OLED are presented using a behavioral language for analog systems (Verilog-A), and the accuracy of this model was verified by comparing with the device simulation results.

Impedance spectroscopy (IS) is a powerful method for characterizing the electrical properties of materials and their interfaces. In this study we use IS to investigate the charge carrier injection properties of different anodes and anode treatments in bottom-emitting organic light-emitting diodes (OLEDs). These are ITO-based (indium tin oxide) hetero-layer devices with TPD (N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4-diamine) as hole transporting layer (HTL) and Alq₃ (tris-(8-hydroxyquinoline) aluminum) as emission and electron transporting layer (EML and ETL, respectively). A detailed analysis of the capacitance as function of frequency and DC bias yields information about trapped and interfacial charges as well as the dynamics of injected charges. Furthermore, we use IS to study degradation processes in OLEDs.

The efficiency and stability of blue organic light emitting devices (OLEDs) continue to be a primary roadblock to developing organic solid state white lighting. For OLEDs to meet the high power conversion efficiency goal, they will require both close to 100% internal quantum efficiency and low operating voltage in a white light emitting device.1 It is generally accepted that such high quantum efficiency, can only be achieved with the use of organometallic phosphor doped OLEDs. Blue OLEDs are particularly important for solid state lighting. The simplest (and therefore likely the lowest cost) method of generating white light is to down convert part of the emission from a blue light source with a system of external phosphors.2 A second method of generating white light requires the superposition of the light from red, green and blue OLEDs in the correct ratio. Either of these two methods (and indeed any method of generating white light with a high color rendering index) critically depends on a high efficiency blue light component.3

Inserting an ultra-thin interlayer has been an important means in modifying the performance of organic semiconductor devices. Using photoemission and inverse photoemission spectroscopy (UPS, XPS and IPES), we have investigated the electronic structure of a number of insertion layers widely used in organic semiconductor devices. We found that inserting alkali metal compound thin layers such as LiF between the electron transport layer (ETL) and the cathode can induce energy level shift in the ETL that reduces the electron injection barrier. The reduction is attributed to the release of the alkali metal that n-doped the ETL, and as such it depends on the cathode material deposited on top of the insertion layer. For thin metal oxide insertion layers, such as MoO₃, between the anode and the hole transport layer (HTL), reduction of the hole injection barrier is also observed. This reduction, however, is due to the large workfunction of the oxide that subsequently moves the highest occupied molecular orbital (HOMO) toward the anode Fermi level. Effects of other insertion layers, such as metal insertion layer in organic bistable device (OBD) and organic insertion layer in bipolar organic thin film transistors (OTFT) will also be discussed.

Turn on voltage in the current density-voltage characteristics is one of the important factors to evaluate the performance of organic light emitting diodes (OLEDs). In this paper, we report investigation of the origins of turn-on voltage, defined at where log J (current density) has a sharp rise and starts to increase dramatically. In OLEDs with NPB as the hole transport layer (HTL) and Alq3 as the electron transport layer (ETL), we find that the turn on voltage is always at 2V, regardless the cathode structures, such as Ca, Al, LiF/Al, and Cs₂CO₃/Al, being used. The turn on voltage is also independent on the thickness of organic layers. Beside NPB and Alq₃, we also study the J-V characteristics on OLEDs with various combinations of HTLs and ETLs. In all the devices investigated, the turn on voltage just equals to the difference between the LUMO of ETL and the HOMO of HTL, taking into consideration of vacuum level shift at organic interfaces measured from the ultraviolet photoemission spectroscopy (UPS). Combined with J-V characteristics of OLEDs and UPS measurement, we propose that the turn on voltage of organic light emitting devices is determined by the difference between LUMO of ETL and HOMO of HTL and is independent of the cathode and thickness of organic layers. We also found that the charge transfers at the interface of ETL/HTL play an important role to the turn on voltage of OLEDs.

The authors review the technological trends for the future AMOLED, especially for unique applications to small- and medium-sized displays as well as large-sized AMOLED TV. The unique characteristics of AMOLED enable paper-thin, foldable, bendable and transparent displays which the other display technology can't easily realize. For large-sized AMOLED TV, TFT backplane, color patterning and encapsulation are the key technological issues and the new technologies should be developed for the mass production of AMOLED TV. The issues and some candidate technologies which can pave the way for mass production of AMOLED TV are also briefly reviewed.

High resolution OLED-on-silicon microdisplay technology is unique and challenging since it requires very small subpixel dimensions (~ 2-5 microns). eMagin's OLED microdisplay is based on white top emitter architecture using small molecule organic materials. The devices are fabricated using high Tg materials. The devices are hermetically sealed with vacuum deposited thin film layers. LCD-type color filters are patterned using photolithography methods to generate primary R, G, B colors. Results of recent improvements in the OLED-on-silicon microdisplay technology, with emphasis on efficiencies, lifetimes, grey scale and CIE color coordinates for SVGA and SXGA resolution microdisplays is presented.

Improving light extraction for OLED devices will be pivotal for their acceptance into the marketplace. Incorporating nanostructures within the high refractive index regions of the OLED multi-layer stack results in an over two-fold improvement in light extraction efficiency. Such nanostructures were made using roll-to-roll fabrication processes. We will also discuss the performance characteristics of the nanostructures on color-angularity and blurring of high-resolution pixels.

We demonstrate the feasibility of white organic light-emitting diodes that exclude the transparent conductor indium-tinoxide. Instead, a highly conductive Orgacon^TM PEDOT:PSS material in combination with a metal support structure is used as transparent anode and hole-injection layer. The PEDOT:PSS exhibits a conductivity of 460±20 S/cm and a work function of 5.35±0.05 eV. On ITO-free OLEDs on glass with an active area of ~6 cm² the inclusion of 120 nm thick printed metal lines reduces the variation in brightness from 35% to 20%. The ITO-free concept based on PEDOT:PSS with printed metal structures is scaled up to large flexible OLEDs with a size of 150 cm² on a heat-stabilized Teonex® Polyethylene Naphtalate foil. The voltage distribution across the various electrodes was verified by a finite element model, allowing a prediction of the OLED brightness and homogeneity over large areas.

High-efficiency is strongly desired for organic light-emitting diodes (OLEDs) to be fully realized as the future display and lighting technology. To replace current illumination tools, such as incandescent bulbs and fluorescent tubes, for examples, OLEDs with much higher efficiency are demanded. We will present herein some approaches for fabricating high-efficiency OLEDs of blue and white emission. Besides employing highly efficient electroluminescent guests and thin device architecture, low injection barriers to carriers, high carrier-transporting character, effective carrier/exciton confinement, balanced carrier-injection, exciton generation on host, effective host-to-guest energy-transfer and improved light-coupling efficiency are essential. Amongst, the incorporation of nano-dots in emissive- and non-emissive-layers can markedly improve the device efficiency. The enhancement is especially marked as small polymeric nano-dots are incorporated into the non-emissive layers. Since the incorporation is not in the emissive layer, the efficiency improvement mechanism works for both fluorescent and phosphorescent devices. Importantly, the efficiency improvement is also a strong function of the surface charge density of the nano-dots. Regardless positively or negatively charged, the improvement becomes more pronounced as the charge density increases. Results regarding some lately achieved extraordinarily highly-efficient OLEDs containing nano-dots with high surface charge will be presented.

AMOLED(active matrix OLED) is known as the next generation display technology due to its better display quality, thin form factor, lower power consumption, etc. With increasing demand of environment-friendly technology, OLED had become a green solution for display. Additionally, due to its simple device structure, extra function could be easily integrated. In this paper, in-cell touch AMOLED is also described briefly.

Organic light emitting devices (OLEDs) are projected to provide a low-cost, long-lived, and efficient wide area lighting solution if challenges in reliability, cost, and efficiency can be overcome. Development of new transparent conducting oxides (TCOs) that do not contain indium for use as the anode in bottom-emitting OLEDs can lead to cost savings and provide longer device lifetimes. Indium-free TCOs need to meet or exceed performance targets including high conductivity and visible light transmission, acceptable stability and, for blue or white OLEDs, a high work function to match the deep HOMO of the hole transport material. In this work, we report results from our efforts to scale up sputter deposition on large area substrates (up to hundreds of cm²) of a Ga-doped ZnO TCO having a composition identified using combinatorial methods. We present the results of initial scale-up efforts and evaluate relevant properties for these films. Finally, we have incorporated these materials in the production of OLEDs, and show performance comparisons between devices fabricated on the scaled-up GZO and commercial indium tin oxide (ITO). The results demonstrate that we are able to generate substrates with the appropriate work function to reduce the operating voltage of blue phosphorescent OLEDs compared to commercial ITO. This work function-HOMO energy matching leads to more efficient charge injection into the device hole transport layer.

We have fabricated transparent white organic light emitting diode (WOLED) for lighting application based on a hybrid white OLED and a phosphorescence white OLED. For the hybrid WOLED, a blue fluorescence emitting layer (FLEML) and green and red phosphorescence emitting layers (PH-EMLs) have been used in the device structure of ITO/hole transporting layer (HTL)/PH-EMLs/interlayer/FL-EML/ETL/LiF/Al. The balanced emissions from the FLEML and the PH-EMLs have been obtained by using appropriate carrier (hole) trapping effects in the PH-EMLs, which resulted in external and power efficiencies of 15 % and 27 lm/W, respectively, at a luminance of 1000 cd/m² without any out-coupling enhancement. The Commission Internationale de L'Eclairage (CIE) coordinates of this hybrid WOLED is (0.43,0.44) with color rendering index (CRI) of 80 and correlated color temperature (CCT) of 3200 K, respectively, in the bottom emission structure. Based on this hybrid WOLED, we established highly efficient transparent WOLED by introduction of a transparent cathode, and obtained over 19 lm/W of power efficiency at a total luminance of 1000 cd/m² as well as over 60 % of transmittance at 550 nm with the conventional glass encapsulation. Moreover, when the phosphorescent white OLED was combined with a transparent cathode, the power efficiency was reached up to 24 lm/W of power efficiency at a total luminance of 1000 cd/m².

The light emitting efficiency and the stability of the phosphorescent devices, whose emission characteristics are strongly dominated not only by the energy transfer but also by the charge carrier trapping influenced by the heterostructured emissive layers and charge injection layer, are studied in terms of the charge injection behavior, carrier transporting mobility, and balancing of devices. The enhancement of the light emitting properties (higher efficiency and lower driving voltage) by use of heterostructures at emitting layer, either multilayers or mixing of hole- and electron-transporting materials (such as 4,4",4"-tris(N-carbazolyl)-triphenylamine); TCTA and bis(10-hydroxybenzo[h]quinolinate) beryllium; Bebq₂) was characterized. By a design of emitting layer structure for recombination, 30~50lm/W efficiency of devices with Ir(ppy)₃ and conventional transporting layer was possible.

We report studies on blue and white organic light-emitting devices (OLEDs) based on the deep-blue electrophosphorescent dye iridium(III) bis(4',6'-difluorophenylpyridinato)tetrakis(1-pyrazolyl)borate (FIr6). Using high triplet energy charge transport layers and a dual-emissive-layer structure as well as the p-i-n device structure, we have achieved external quantum efficiencies of 20% and maximum power efficiency of 36 lm/W in these deep-blue OLEDs. White OLEDs with a CRI of 79 and a maximum power efficiency of 40 lm/W were also demonstrated by incorporating red and green phosphorescent dopants together with FIr6.

Organic light emitting devices (OLEDs) have demonstrated the potential for solid state lighting as well as full color display applications. Use of triplet harvesting phosphorescent materials has led to very high efficiency OLEDs especially in green and red phosphorescent OLEDs. However in case of blue OLEDs the efficiency achieved is still room for improvement. Charge balance is a very important factor for achieving high efficiency organic light emitting diodes. In most OLED devices, hole mobility of hole transport layer is orders of magnitude higher than the electron mobility of electron transport layer. We study how this affects the charge balance and hence the device performance in the blue phosphorescent OLEDs with Iridium (III)bis [(4,6-di-fluorophenyl)- pyridinato-N,C2´] picolinate (FIrpic) emitter. Charge balance is studied in these devices and the devices are found to be hole dominant. Additionally, effect of charge balance on device performance is demonstrated with different electron transport layers. Using this approach, a very high efficiency of 60 Cd/A (50 lm/W) is achieved with 3,5´-N,N´-dicarbazole-benzene (mCP) host.

Vertical type organic light emitting transistors (OLETs), which combined with the organic static induction transistors (OSITs) as the vertical type organic transistors and conventional organic light emitting diodes (OLEDs), are promising for flexible sheet displays. In our recent research, pentacene based OSITs fabricated on flexible plastic substrates exhibited stable electrical characteristics under bending condition. However, several problems have remained in the OSITs with low on/off ratio and low current value for use in the vertical type OLETs. This paper describes our recent efforts to improve the performance of vertical type OLETs by optimizing the device structure and organic materials used in the OSITs. Interface between organic source electrode and semiconductor is important factor to control the device operation of vertical type organic transistors. CuPc layer was inserted between ITO source electrode and pentacene film in order to improve the performance of OSITs. The results showed that both the high on/off ratio more than 103 and the high current value of larger than 40 μA were achieved. In addition, vertical type OLET and logic devices were fabricated using the OSITs for the realization of flexible sheet displays. These results exhibit that the OSITs attract attention for application in organic flexible displays.

In this contribution we emphasise the ambipolar organic field-effect transistors (OFETs) as the prime element for the realization of various OFET types. It will be shown that ambipolar OFETs can be used to produce on the one hand complementary unipolar OFETs and thus CMOS elements and on the other hand light-emitting OFETs. Some ambipolar light-emitting OFETs will be presented and the impact of the contact formation at the source and drain electrodes on the device characteristics will be discussed. In general, the investigation of ambipolar OFETs provides a deep understanding of the OFET operation and guides the way to novel aspects of the OFET applicability.

Solid-state dye-doped polymeric distributed-feedback lasers in near-infrared wavelength region were fabricated by photo nanoimprint lithography. Fluorinated-polyimide material which shows low propagation loss in the near infrared was used as the host matrix of the active waveguide doped with near-infrared organic dye, LDS950. Single wavelength lasing emission at 953 nm, which corresponds to the second-order Bragg reflection for the grating, was observed at room temperature from the laser by photo-pumping using nitrogen-gas laser. When the ambient temperature is raised, the lasing wavelength shifts to shorter at a ratio of 0.094 nm/K between 20 and 50°C, as the effective refractive index of the active region becomes smaller. The lasing threshold pumping density stays nearly constant during the temperature variation.

Efficient white OLEDs are becoming attractive as large area light sources for illumination and in future also for general lighting. We discuss device concepts for white OLEDs and their potential to achieve high efficacy and good lumen- and color-maintenance at the same time. We focus on OLEDs using a combination of fluorescent blue and phosphorescent red and green emitters (hybrid OLEDs). Hybrid OLEDs have high efficacy and lifetime in the white to warm white color region (color points B and A on the black-body-curve). Near illuminant A efficacy values of 28-29 lm/W without optical out-coupling can be achieved with a hybrid OLED. The external quantum efficiency (EQE) is 14%. A typical color rendering index (CRI) is 84. Recent results for monochrome OLEDs and for hybrid OLED stacks are presented.

The internal quantum efficiency of organic light-emitting diodes (OLEDs) can reach values close to 100% if phosphorescent emitters to harvest triplet excitons are used, however, the fraction of light that is actually leaving the device is considerably less. In this work we use numerical simulations to optimize light outcoupling from different OLED stacks. First, we change the distance of the emission zone to the cathode, which minimizes the excitation of surface plasmons. Then the influence of different dipole orientation of the emitter material on the light outcoupling is studied. Finally, a metal-free, transparent OLED stack reported by Meyer et al.,¹ where no plasmons can be excited, is investigated for improved outcoupling efficiency.

Thin organic film is coated on the laser absorbing layer. The organic material coated heat absorbing layer is closely contacted with the substrate. When the laser is incident on the heat absorbing layer, the absorbing layer is expanded and the organic film is transferred to the substrate. When the laser has Gaussian spatial profile, the profile of printed organic material becomes non-uniform. We tried several laser beam profile shaping methods to get a clean and sharp printing. The dependences of eliminated organic material profile from donor plate on the laser power, beam shaping method, and the layer thickness are also investigated.

The dynamical degradation process of operating organic light-emitting diode (OLED) was proposed and investigated by non-destructive reflectivity measurements using a p-polarized He-Ne laser as probing tool. The intrinsic OLED degradation mechanism mainly depends on intermediate layers at organic/electrode interfaces. The optical behavior of these interfacial dielectric layers and corresponding optical parameters may be capable of representing OLED degradation in macroscopic aspect. Optical parameters defined as optical constants (n, k) and thickness (d) were obtained from fitting our experimental data to a theoretical model including interfacial dielectric layers with (n, k, d) as adjustable parameters. Our experimental results revealed that the change of the reflectivity spectra obtained from static and operated OLED was observable. The tendency of change in reflectivity spectra can be used as qualitative and dynamical aspect of degradation of operating OLED. The dynamical degradation process can be quantitatively modeled by inspecting the variation of optical parameters. This dynamical aspect may also include time-dependent information of degradation as operating OLED. Our data-fitting results indicated that optical constants of intermediate layers have a trend to increase as OLED from static to turn-on status. The thickness of intermediate layers obtained from data-fitting ranged from 0.2 to 14nm, satisfying our expectation. The reflective spectra obtained from basic OLED with ITO/Alq₃/LiF/Al structure revealed a clear dip located around 61.5° incident angle from ITO glass side as OLED in turn-on status. It indicated that surface plasma resonance may occur even in OLED layer structure.

Efficient solid-state emission of organic materials is essential for optoelectronic devices such as organic light-emitting diodes, light-emitting thin film transistors, semiconductor lasers, and solid luminescent sensors. Therefore, exploration of novel chromophores that emit visible light with high efficiency in the solid state and understanding of their characteristics regarding molecular and electronic structures as well as three-dimensional arrangement in the solid state are highly important for the development and advance of such optoelectronic devices. We will report synthesis, structures, and photophysical properties of 3,2'-silicon-bridged 2-arylindoles that exhibit blue and greenish blue photoluminescence with high to excellent quantum yields (0.65~1.0) in the solid states such as microcrystals, thin-film, and doped polymer film. In addition, synthesis and photophysical properties of 1,4-bis(alkenyl)-2,5-dipiperidinobenzenes that are compact and highly emissive solid fluorophores will be also presented. The emission colors of the benzenes can be tuned in a range from blue to red by choosing appropriate functional groups incorporated at the ethenyl moieties.

Recently, we have presented optically-pumped edge-emitting organic laser devices consisting of Alq3:DCM film (5% DCM) deposited onto a polished GaAs (100) substrate coated with an 1-um-thick layer of RF sputtered SiO₂ using cleaving method. The threshold density was typically 3 μJ/cm² in a sample with a cavity length of 5 mm. The internal loss α and the gain coefficient β were found to be about 10.5 cm^-1 and 3.2 cm-μJ^-1, respectively. BSB-Cz has quite-high efficiency as blue laser material. In this work, organic laser devices of CBP:BSB-Cz film (6% BSB-Cz) were vacuum-deposited onto a polished GaAs (100) substrate coated with an 1 um-thick layer of RF sputtered SiO₂. The cleaved samples were optically pumped by a N₂ gas laser (wavelength: 337 nm) with a pulse width of 600 ps at a repetition rate of 20 Hz. We investigated emission spectrum, emission intensity and the full width at half maximum (FWHM) by varying excitation intensity. Pumping a sample with a cavity-length of 5 mm, emission intensity drastically increased at certain. The FWHM drastically narrowed as the emission intensity was increased. The threshold density was 1.40 μJ/cm² with a cavity length of 5 mm, it was half as much as Alq3:DCM. The internal loss α and the gain coefficient β were found to be about 5.57 cm^-1 and 6.72 cm-μJ^-1. We found BSB-Cz material have higher efficiency than Alq3:DCM. Moreover, polarization characteristics. And the threshold density cavity length relationship were investigated.

There have been many researches regarding to the organic light-emitting diodes (OLEDs) with microcavity structures, in order to enhance its output optical properties such as chromaticity and intensity. In the applications to the white-light OLED (WOLED) and full color displays, the difficulty remains in the design of the optical length of the microcavity for proper resonance. A typical microcavity structure consists of the dielectric quarter wave stacks (QWS) as a distributed Bragg reflector (DBR) and the metal cathode to form a pair of mirrors. The organic and other material layers between the mirrors plays the role of the cavity. It can only have one major resonance peak in the perpendicular view angle and degrade the broad spectrum nature of the WOLED. Our study proposes the use of non-QWS mirror using thicker and higher-order (greater integral multiple of the quarter wavelength) of the dielectric layers. We can have the multiple resonance peak wavelengths to meet the WOLED requirement by introducing the reflection phase change of the dielectric stack mirror at certain wavelengths. The proposed microcavity structure yields a desired shift to the white point in CIE chromaticity for a typical green OLED. One of the potential applications of the microcavity with non-QWS mirror can be to make the WOLED even closer to the CIE white point without worrying the doping process variation, which is a typical problem in the WOLED. It greatly enhances the usability of the WOLED in various applications.

We use dark-injection space-charge-limited current (DI-SCLC) and admittance spectroscopy (AS) to study charge injection and transport properties of spiro-linked arylamine compounds. Examples are spiro-linked TPD and spiro-linked NPB which are both important amorphous hole transporters for organic light-emitting diodes (OLEDs). With PEDOT:PSS as the hole-injection layer, the contact is demonstrated to be generally Ohmic. Both techniques can be used to measure the carrier mobilities of thick films (>μm) of spiro-compounds. DI-SCLC can be viewed as a pulse technique whereas AS can be treated as an ac technique. For the hole mobilities evaluation of the spiro-compounds, both techniques are in general agreement to each other. However, for the case of the thinner films of less than 1μm, AS is superior over the DI-SCLC technique. The advantages of AS will be highlighted. It appears that AS is broadly applicable to characterize transport properties of organic thin films.

The emission properties of polymer light-emitting diode (PLEDs), using blue emissive poly(9,9-dioctylfluorene) (PFO) and yellow-green emissive poly[9,9-dioctylfluorenyl-2,7-diyl)-co-1, 4-benzo-{2,1'-3}- thiadiazole)] (F8BT) fabricated by the spin-coating method, the toluene vapor method and the thermal printing method, were investigated. poly(2,7-(9,9-din-octylfluorene)-alt-(1,4-phenylene-( (4-sec-butylphenyl)imino)-1,4-phenylene)) (TFB) is useful for buffer layer and a dopant when we use the spin-coating method. When we use TFB as interlayer of PLED, TFB acts as exciton-blocking layer, thus prevents luminescence quenching. When we use TFB with 2-(4-biphenylyl)-5-phenyl-1,3,4-oxadiazole (PBD) as dopants of PFO, better current efficiency was achieved, compared to PFO only device. This result derives from these materials working as hole and electron transporting molecules. The blue and yellow-green PLEDs fabricated by the spincoating method showed maximum efficiencies of approximately 1.1 and 1cd/A, respectively. The device with bis[1-(9,9-dimethyl-9H-fluoren-2-yl)-isoquinoline](acetylacetonate)iridium(III) (Ir(fliq)2acac) doped in PFO showed red-emission and a maximum efficiency of approximately 1cd/A. Current efficiencies of PLEDs with the β phase of PFO fabricated by the thermal printing method and the toluene vapor method were found to have better emission efficiency than that with the amorphous phase of PFO by the spin-coating method. The EL spectra of PLEDs using PFO and PFO:F8BT fabricated by the thermal printing method were polarized. The transient characteristics of PLEDs using β phase of PFO were better than amorphous phase of that. It is expected to improve the characteristics of PLEDs by the optimization of the thermal printing method. We demonstrated improved light emission of PLEDs with the high-quality β phase by the thermal printing method.

We report white electroluminescence from a single component-single layer solution processed organic light emitting diodes (OLEDs). In this work, we have fabricated and characterized OLEDs based on a single polymer synthesized by incorporating a small amount of the orange-light emitting chromophore 1,8-Naphtalimide derivative as side chain to poly(fluorene-alt-phenylene) (PFP). The structure of the devices is ITO/PEDOT:PSS/Active layer/Al. The dopant unit was convalenttly attached to the side chain of polyfluorene by alkyl spacers. We have fabricated devices with different amounts of the orange chromophore (0, 0.0005, 0.005, 0.02 and 0.08 in weight) as well as a device based on a physical blend in the same proportion of 0.08 for comparison purposes. Absorption and Photoluminescence (PL) studies in thin films show no significant interaction can be observed between both moieties in the ground state, but after photoexcitation an efficient energy transfer takes place from PFP to the orange chromophore. We have observed a more efficient energy transfer in these compounds than for physical mixtures of the two chromophores due to a phase separation effect in the blend confirmed by the optical measurements and ESEM analysis, obtaining energy transfer even in diluted solutions from the intramolecular interaction in the copolymers. With this very simple device structure, white light with Commission Internationale de l'Eclairage (CIE) coordenates (0.34;0.43) is obtained for the electroluminescence (EL) emission and turn on voltage of 6 V for the device based on the copolymer with x = 0.02, together with a good match in the EL and PL spectra indicative that two emissions are produced by the same species, making this material very suitable for large area solution processed devices in solid state illumination.

Two novel approaches are reported to significantly enhance the conductivity of transparent PEDOT:PSS (PEDOT:PSS = poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)). The first method is to add anionic surfactants into aqueous solution of PEDOT:PSS. Conductivity enhancement by a factor of hundreds was observed, and it was strongly dependent on the chemical structure of the surfactant. Conductivity enhancement from 0.16 S cm-1 to 80 S cm-1 was observed, when anionic surfactant SDS was added. The effect of the anionic surfactants on the conductivity of PEDOT:PSS was attributed to the substitution of the PSS anions by the surfactant anions. The addition of a nonionic surfactant had moderate effect on the conductivity of PEDOT:PSS, while cationic surfactant almost did not affect the conductivity. The second method to significantly enhance the conductivity is to treat the PEDOT:PSS film with solutions of certain salts. CuCl2 or InCl3 solution could enhance the conductivity by a factor of hundreds, while the effect by NaCl is negligible. The salt effect on the conductivity of PEDOT:PSS is attributed to the loss of PSS from PEDOT:PSS and conformational change of PEDOT chains during the treatment.

The band alignment at metal-organic interfaces has been extensively studied; however the electrodes in real devices often consist of metals modified with dielectric buffer layers. We demonstrate that interface dipole theory, originally developed to describe Schottky contacts at metal-semiconductor interfaces, can also accurately describe the injection barriers in real organic electronic devices (i.e, at electrode-organic interface). It is found that theoretically predicted hole injection barriers for various archetype metal-organic and metal-dielectric-organic structures are in excellent agreement with values extracted from experimental measurements.

Tandem white organic light emitting diodes (WOLEDs) are fabricated with blue and red unit devices connected by a transparent Al:LiF/molybdenum oxides (MoO₃) connecting layer. The blue and red unit devices have been fabricated with standard structure based on 8 % iridium (III)bis(4,6-(di-fluorophenyl)-pyridinato-N,C2') picolinate (FIrpic) doped in N,N'-dicarbazolyl-3,5-benzene (mCP) and 8 % bis (1-phenylisoquinolinato-N,C² )iridium(acetylacetonate) ((piq)2Ir(acac)) doped in 4,4'-N,N'-dicarbazolebiphenyl (CBP), respectively. The doping concentration of LiF in the Al:LiF composite layer is 10 % and the Al:LiF layer thickness is varied from 3 nm up to 10 nm to optimize the performance of tandem WOLEDs while the MoO3 thickness is fixed at 10 nm. We found that electron injection efficiency decreases for thicker Al:LiF layer, resulting lower electroluminescence (EL) efficiency. The maximum brightness and current luminous efficiency for the tandem WOLEDs are about 32,230 cd/m² and 18.5 cd/A, respectively, for the Al:LiF (10 %) thickness of 3 nm.

A comprehensive photoluminescence (PL)-detected magnetic resonance (PLDMR) study of various vacuum-sealed rubrene films and powders is described. Three PLDMR features are observed and analyzed: (i) A negative (PL-quenching) triplet exciton (TE) resonance at T > 50K, due to reduced spin-dependent fusion of geminate TE pairs to singlet excitons (SEs). (ii) A positive (PL-enhancing) triplet resonance at T < 50K. This resonance is suspected to result from reduced quenching of SEs by a reduced population of polarons and nongeminate TEs, the latter due to the spin-dependent annihilation of TEs by polarons. (iii) A negative spin 1/2 (polaron) resonance, believed to be due to enhanced formation of trions at oxygen centers. As single crystal thin films of oxygen-doped rubrene exhibit exceptionally high room-temperature carrier mobility, the relation of this positive resonance to these transport properties is also discussed.

The phosphorescence polymer LEDs (PhPLEDs) with the structure of ITO/PEDOT:PSS/PVK:Ir(ppy)₃: PFO:Ir(pq)₂acac/TPBI/LiF/Al were fabricated to investigate the effect of doping concentrations on the electrical and optical properties of PhPLEDs. The PVK(poly-vinylcarbazole) and Ir(ppy)₃[tris(2-phenylpyridine)iridium(III)] polymers were used as the host and guest materials. The PFO[poly(9,9-dioctylfluorene)] and Ir(pq)₂(acac) [bis(2-phenyl-1-quinoline)iridiumacety lacetonate] were also introduced as other guest materials for the white emission. The Ir(pq)₂acac concentrations was changed ranging from 1.0 to 5.0 volume % (vol %) in the emission layer. The concentration of PVK:Ir(ppy)₃:PFO was fixed with 100:2.0:1.0 in vol %, respectively. The white PhPLEDs were obtained for the samples with 5.0 vol % of Ir(pq)₂acac material and the maximum luminance was found to be 2430 cd/m². The CIE color coordinators were ranged with x, y = 0.32~0.33, 0.33~0.34 at 8V, showing good white color.

The properties of phosphorescent fac tris(2-phenylpyridine) iridium [Ir(ppy3)]-doped poly(N-vinyl carbazole) (PVK)/4,7-diphenyl-1,10-phenanthroline (Bphen) polymer/small molecular hybrid OLEDs are described. For optimal BPhen thickness, the power efficiency of the devices exceeds 30 lm/W. The low-temperature electroluminescence- detected magnetic resonance (ELDMR) exhibits the well-known negative spin 1/2 resonance attributed to enhanced formation of trions, but the positive spin 1/2 resonance, typically observed at low temperature or at high current density, is not observed. The OLEDs' performance and the ELDMR results are discussed in relation to the nature of the defects and their density in these devices.

The electroluminescence (EL)-detected magnetic resonance (ELDMR) of abrupt junction and mixed layer N,N'-diphenyl-N,N'-bis(1-naphthylphenyl)-1,1'-biphenyl-4,4'-diamine (NPB) / tris(quinolinolate) Al (Alq₃) OLEDs was measured at room temperature and at 20K, at current densities 0.83 ≤ J ≤ 83 mA/cm². The abrupt junction and mixed layer devices were indium tin oxide (ITO) / 5 nm copper phthalocyanine (CuPc) / 50 nm NPB / 40 nm Alq₃ / 1 nm CsF / Al, and ITO / 5 nm CuPc / 40 nm NPB / 20 nm 1:1 NPB:Alq₃ / 30 nm Alq3 / 1 nm CsF / Al, respectively. As expected, the devices exhibited a positive (EL-enhancing) spin 1/2 resonance at T = 20 K and a negative (ELquenching) spin 1/2 resonance at room temperature. It was found that the positive and negative resonance was stronger in the abrupt junction and in the mixed layer devices, respectively. The results are discussed in relation to the mechanisms responsible for these resonances, namely reduced quenching of singlet excitons by polarons and triplet excitons, and enhanced quenching by trions, respectively.