This PDF file contains the front matter associated with SPIE Proceedings Volume 8829, including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

We present two classes of host materials for blue phosphors. The first are carbazole substituted biphenyls 1-9. In these CBP-type materials the triplets are confined to one half of the molecules by using either twisted biphenyls or by a metalinkage of the carbazoles to the biphenyl. We obtained high triplet energies of 2.95-2.98 eV and high glass transition temperatures in the range of 100-120 °C. OLEDs were fabricated using the host material 6 and the carbene emitter Ir(dbfmi) with pure blue emission at 450 nm. The devices achieved an external quantum efficiency of 8.7% at 100 cd/m² and 6.1% at 1000 cd/m². MBPTRZ with an electron transporting biscarbazolyltriazine that is separated from the hole transporting carbazole by a non-conjugated, meta-linked biphenyl unit is an example for a bipolar matrix material. The excellent glass forming properties and the high T_g of 132 °C ensure morphological stability in OLEDs. The meta-linkage and the additional twist at the biphenyl unit, which is achieved by two methyl groups in the 2- and 2’-position of the biphenyl in MBPTRZ leads to a decoupling of the electron accepting and electron donating part and therefore to a high triplet energy of 2.81 eV. DFT calculations show a clear separation of the electron and hole transporting moieties. A phosphorescent OLED with MBPTRZ as host and FIrpic as emitter reached a maximum external quantum efficiency of 7.0%, a current efficiency of 16.3 cd/A and a power efficiency of 6.3 lm/W.

A series of highly luminescent mono-, di-, and trinuclear copper(I) complexes has been synthesized using modular ligand systems of easily accessible N^N, P^P or P^N ligands in order to show the rich structural diversity of copper(I) compounds. Those systems allow for the design of various emitting materials with desired photophysical properties, such as emission colors and high efficiencies. The complexes were characterized with well-established methods such as X-ray crystallographic studies or elemental analysis and, in addition, due to their interesting photoluminescence characteristics, their emission properties were further investigated by means of spectroscopic methods as well as DFT-calculations. In detail, various cationic and neutral mononuclear complexes have been synthesized in order to investigate the photophysical properties of this these different types of emitting compounds. It has been found that neutral copper(I) complexes show superior emission properties (with PLQY up to 89%) compared to their cationic counterparts. Furthermore, a series of dinuclear and trinuclear copper(I) complexes has been synthesized featuring an easy tunable emission maximum from sky blue to deep red (481 nm to 713 nm) with extraordinary high photoluminescence quantum yields up to 99%. In addition, a new crosslinking-technique has been developed to open up the door for a new way to fully solution processed OLED using these promising emitting compounds: Alkyne-substituted emitting complexes crosslink automatically with azide-polymers in a copper-catalyzed alkyne-azide Click reaction.

Organic light emitting diodes using Pt-based red, green and blue dopants have been built for application to solid state lighting. All layers were deposited by thermal evaporation. Devices used a stacked design with separate red, green and blue layers. Blue devices achieved external quantum efficiencies of over 16% while devices with red / green / blue emissive layers reached quantum efficiencies of up to 15%, depending on the thickness of the red and green layers. We demonstrate an all-Pt based multiple emissive layer WOLED device.

The preparation of conjugated polymer particles with uniform size is presented and discussed. The particles can selfassemble into photonic crystal arrangements exhibiting a photonic band-gap. This way, active optical assemblies with an optical stop-band and an independent fluorescence band can be fabricated. To showcase the applicability of the particles, which can be processed from dispersion, optical core sheath fibers are presented. The particles can be extruded into the core of the fiber with polyacrylonitrile as the cladding material. The particle dispersions can be easily processed by dryspinning and are confined to only the core of the fiber, where they assemble into a random close packing.

The efficiency improvement of fluorescent blue organic light-emitting diodes were investigated by inserting buffer layer. The OLED device using several buffer materials which have different HOMO and LUMO energy level were evaluated. The inserted buffer layer could control the effective hole injection and electron blocking, which leaded to remarkable high efficiency performance.

Hole transporting behavior of two fluorene derivatives having carbazole group (2C1CBz) and diphenyl amino group (2C1DAF) and a carbazole derivative (C2CBzCBz) were investigated. Further, the fluorene derivatives and typical hole-transporting materials, 4,4’-bis[N-(p-tolyl)-N-phenyl-amino] biphenyl (TPD) and 4,4'-Bis(carbazol-9- yl)biphenyl (CBP) was analyzed based on the Gaussian Disorder Model. At room temperature, amorphous film of 2C1CBz exhibited highest hole mobility of 3.1 x 10^-3 Vcm²/Vs at 1.6 x 10⁵ Vcm^-1 in these materials. From analysis based on the Gaussian Disorder Model, however, amorphous film of CBP is indicated to have highest disorder free mobility; the values of 2C1CBz, 2C1DAF, CBP and TPD were 0.812, 0.092, 2.84, and 0.38 cm²/Vs, respectively. In addition, their reorganization energy / was evaluated by a quantum mechanical calculation with ADF (Amsterdam Density Functional package, Scientific Computing and Modeling Co.) based on the Marcus theory. The experimental and calculation results demonstrated that the u0 has good proportionality relation with the /. Because theu0 mean as a rough standard of carrier-transporting, this result suggest that evaluation of / may be a promising approach to design molecular structure of carrier transporting materials with high carrier mobility.

World’s first commercialized 55-inch WRGB OLED TV has been developed and launched recently. Large-sized OLED displays require novel technologies to realize mass production. We will introduce commercialized 55-inch WRGB OLED TV and its novel technologies including oxide TFT, WOLED, solid phase encapsulation, and compensation technologies.

This study presents a TFT structure which has less photo process and higher cost competitiveness in AMOLED display markets. A novel LTPS based 6 masks TFT structure for bottom emission AMOLED display is demonstrated in this paper. High field effect mobility (PMOS < 80 cm²/Vs ) and high reliability (PBTS △Vth< 0.02V @ 50oC VG=15V 10ks) was accomplished without the high temperature and rapid thermal annealing (RTA) activation process. Furthermore, a 14-inch AMOLED TV was achieved on the proposed 6-pep TFT backplane using the Gen. 3.5 mass production factory.

Three new solution processable small molecular host materials based on bis-[3,5-di(9H-carbazol-9-yl)phenyl] structural moiety have been developed for blue phosphorescence (FIrpic dopant) organic light-emitting diodes. Whereas N,N-bis-[3,5-di(9H-carbazol-9-yl)phenyl]methylamine (CzPAMe) has the highest solid state triplet energy gap (ET) of 2.73 eV, tetrakis-[3,3',5,5'-(9H-carbazol-9-yl)]triphenylphosphine oxide (CzPPO) and N,N-bis-[3,5-di(9H-carbazol-9-yl)phenyl]pyrimidin-2-amine (CzPAPm) are two host materials potentially being bipolar for charge transport due to the electron deficient unit of phenylphosphine oxide and pyrimidine, respectively. Due to the insufficient ET (2.56 eV) of CzPAPm, CzPPO or CzPAMe devices are significantly better than CzPAPm devices with or without 1,3-bis[(4-tert-butylphenyl)-1,3,4-oxadiazolyl]phenylene (OXD-7) co-host. Particularly, having no OXD-7 co-host and no vacuum-thermal-deposited extra electron transporting layer, single-layer devices of CzPPO surpassing CzPAMe devices reach current efficiency as high as 9.32 cd/A (or power efficiency of 4.97 lm/W), which is one of the highest of the kind. Corresponding single-layer white phosphorescence OLEDs are also fabricated with the small molecular host material demonstrated herein.

Herein we report on the fabrication and the properties of two highly efficient blue light emitting multilayer polymer light emitting diodes (PLEDs). The first device structure combines a thermally stabilized polymer with a material processed from an orthogonal solvent, allowing for the fabrication of a triple layer structure from solution. The well known poly(9,9-dioctyl-fluorene-co-N-(4-butylphenyl)-diphenylamine) (TFB), which can be stabilized in a bake-out procedure, was used as a hole transporting layer. A novel pyrene – triphenylamine (PPyrTPA) copolymer was used as emissive layer. The stack was finalized by a poly(fluorene) - derivative with polar side-chains, therefore being soluble in a polar solvent which allows for the deposition onto PPyrTPA without redissolving. The resulting PLED showed bright-blue electroluminescence (CIE1931 coordinates x=0.163; y=0.216) with a high efficiency of 1.42 cd/A and a peak luminescence of 16500 cd/m². The second presented device configuration comprises a thermally stabilized indenofluorene – triphenylamine copolymer acting as hole transporter, and an emissive copolymer with building blocks specifically designed for blue light emission, effective charge carrier injection and transport as well as for exciton generation. This multilayer PLED led to deep-blue emission (CIE1931 x=0.144; y=0.129) with a remarkably high device efficiency of 9.7 cd/A. Additionally, atomic force microscopy was carried out to investigate the film morphology of the components of the stack and x-ray photoemission spectroscopy was performed to ensure a full coverage of the materials on top of each other. Ultraviolet photoemission spectroscopy confirmed the desired type-II band level offsets on the individual interfaces.

Polymer micro- and nano-fibers, made of organic light-emitting materials with optical gain, show interesting lasing properties. Fibers with diameters from few tens of nm to few microns can be fabricated by electrospinning, a method based on electrostatic fields applied to a polymer solution. The morphology and emission properties of these fibers, composed of optically inert polymers embedding laser dyes, are characterized by scanning electron and fluorescence microscopy, and lasing is observed under optical pumping for fluences of the order of 10² μJ cm^-2. In addition, lightemitting fibers can be electrospun by conjugated polymers, their blends, and other active organics, and can be exploited in a range of photonic and electronic devices. In particular, waveguiding of light is observed and characterized, showing optical loss coefficient in the range of 10²-10³ cm^-1. The reduced size of these novel laser systems, combined with the possibility of achieving wavelength tunability through transistor or other electrode-based architectures embedding nonlinear molecular layers, and with their peculiar mechanical robustness, open interesting perspectives for realizing miniaturized laser sources to integrate on-chip optical sensors and photonic circuits.

We report progress in the development of a new technique that has the potential to enable the vacuum deposition of OLEDs with feature sizes ≤ 20um, and hence high resolution OLED displays. An OLED device with 16um by 130um sub-pixel size has been successfully demonstrated utilizing the novel idea of the in-situ shadow mask patterning method showing the capability to achieve high resolution OLED patterning. In the approach proposed here, two sheets of polyimide film are mounted on the bottom electrode of an OLED. The top sheet of the two stacked sheets is patterned insitu by laser ablation to create apertures to function as a deposition shadow mask. The lower sheet, which serve as a protective layer to the electrode during the laser ablation step is then removed, and OLED materials are deposited through the now patterned top sheet. Since mask alignment is not required in this approach, the technique circumvents the resolution limitations imposed by the difficulty of aligning shadow masks in the conventional techniques, and allows achieving high resolution pixel patterning. Furthermore, shadow effects, another factor that limits resolution in conventional techniques, can be reduced due to the use of very thin polyimide film (~7.5um) that is directly held on the substrate by electrostatic force. In principle, by applying this technique to the standard three color side-by-side sub-pixel matrix scheme, a resolution and aperture ratio of 338ppi and 60%, respectively, can be expected, which is estimated based on the fact that the width of the deposited material is 25um for the 16um wide electrode.

Candles emit sensationally-warm light with a very-low color-temperature, comparatively most suitable for use at night. In response to the need for such a human-friendly night light, we demonstrate the employment of a high number of candle light complementary organic emitters to generate mimic candle light based on organic light emitting diode (OLED). One resultant candle light-style OLED shows a very-high color rendering index, with an efficacy at least 300 times that of candles or twice that of an incandescent bulb. The device can be fabricated, for example, by using four candle light complementary emitters, namely: red, yellow, green, and sky-blue phosphorescent dyes, vacuum-deposited into two emission layers, separated by a nano-layer of carrier modulation material to maximize both the desirable very-high color rendering index and energy efficiency, while keeping the blue emission very low and red emission high to obtain the desirable low color temperature. With different layer structures, the OLEDs can also show color tunable between that of candle light and dusk-hue. Importantly, a romantic sensation giving and supposedly physiologically-friendly candle light-style emission can hence be driven by electricity in lieu of the hydrocarbon-burning and greenhouse gas releasing candles that were invented 5,000 years ago.

For OLEDs to become a mainstream technology, all major display companies are ramping up their efforts to enable cost efficient manufacturing on larger substrate sizes and higher throughput. This puts additional pressure on the suppliers of respective manufacturing equipment to address perceived challenges for scaling and throughput. This paper discusses perceived challenges in today’s manufacturing and how Organic Vapor Phase Deposition (OVPD®) can address these.

Flexible OLED light sources have great appeal due to new design options, being unbreakable and their low weight. Top-emitting OLED device architectures offer the broadest choice of substrate materials including metals which are robust, impermeable to humidity, and good thermal conductors making them promising candidates for flexible OLED device substrates. In this study, we investigate the bending limits of flexible top-emitting OLED lighting devices with transparent metal electrode and thin film encapsulation on a variety of both metal and plastic foils. The samples were subjected to concave and convex bending and inspected by different testing methods for the onset of breakdown for example visible defects and encapsulation failures. The critical failure modes were identified as rupture of the transparent thin metal top electrode and encapsulation for convex bending and buckling of the transparent metal top electrode for concave bending. We investigated influences from substrate material and thickness and top coating thickness. The substrate thickness is found to dominate bending limits as expected by neutral layer modeling. Coating shows strong improvements for all substrates. Bending radii <15mm are achieved for both convex and concave testing without damage to devices including their encapsulation.

The light emission from an electrical dipole antenna is determined by the orientation of the antenna and the optical properties of the materials that surround it. For the outcoupling efficiency of an OLED it is beneficial if the dipole moment of the luminescent transition is parallel with the substrate. In some OLEDs a preferential orientation of the emitting molecules can indeed be observed. In this paper we discuss how anisotropy of the dipole orientation and optical anisotropy of the materials influence the light emitted from a planar structure. Numerical simulations are verified with measurements of OLEDs (for the dipole orientation) and dye doped liquid crystals (for the optical anisotropy).

Bragg scattering by one dimensional periodic structures is investigated in order to enhance the outcoupling effciency of optically optimized planar top-emitting OLEDs. Using a soft imprint process, we fabricate extremely homogeneous gratings with sub- m period. These gratings are integrated beneath the bottom contact of topemitting OLEDs, without affecting the electrical device performance. The reflective contacts of the top emission geometry introduce pronounced micro-cavity effects for directly outcoupled and internally trapped light modes. Bragg scattering of the trapped waveguided and surface plasmon modes into the air cone, i.e. the forward direction, leads to interference with the directly outcoupled mode. As a result, constructive and destructive interference of the modes is detected and analyzed. Overall, we find that the introduction of shallow one dimensional sub- m periodic grating structures underneath top-emitting OLEDs leads to an EQE and luminous efficacy enhancement by up to 42%.

A general challenge in Organic Light Emitting Diodes (OLEDs) is to extract the light efficiently from waveguided modes within the device structure. This can be accomplished by applying an additional scattering layer to the substrate which results in outcoupling increases between 0% to <100% in external quantum efficiency. In this work, we aim to address this large variation and show that the reflectivity of the OLED is a simple and useful predictor of the efficiency of substrate scattering techniques without the need for detailed modeling. We show that by optimizing the cathode and anode structure of glass based OLEDs by using silver and an ITO free high conductive Agfa Orgacon™ PEDOT:PSS we are able to increase the external quantum efficiency of OLEDs with the same outcoupling substrates from 2.4% to 5.6%, an increase of 130%. In addition, Holst Centre and partners are developing flexible substrates with integrated light extraction features and roll to roll compatible processing techniques to enable this next step in OLED development both for lighting and display applications. These devices show promise as they are shatterproof substrates and facilitate low cost manufacture.

We report extremely high light out-coupling efficiency from a transparent organic light-emitting diode (OLED) integrated with microstructures on both sides of the device.[1] The OLED having a metal free structure offers dramatically reduced surface plasmonic loss and absorption loss. To extract the confined light inside the device, a high refractive index light extraction pattern was directly fabricated on the top side transparent conducting oxide electrode using a simple evaporation method, and a micro lens array sheet was simultaneously attached on the bottom side of the glass substrate. As a result, the external quantum efficiency of the device increased from 18.2% to 47.3% by using the microstructures, and was additionally enhanced to 62.9% by attaching an index-matched hemisphere lens instead of the micro lens array on the glass side in order to reduce additional light guiding loss inside of the device. These values showed very good agreement with the simulation performed by a combination of the dipole model and a 3-dimensional geometrical simulation.

A new series of mixed ligand platinum(II) complexes with a formula of FPtXND, where XND = 4-hydroxy-1,5-naphthyridine derivates and F = 2-(2,4-difluorophenyl)pyridine, were newly synthesized, and their photophysical properties were examined. Single crystal X-ray diffraction of FPtOPhND were determined to elucidate their variation of solid state phosphorescence and electroluminescence. Organic hole transporting as well as blue light-emitting NPB (1-naphthylphenylbiphenyl diamine) or 4P-NPD (1-naphthylphenylquaterphenyl diamine) was employed in the platinum complex-based hybrid white organic light emitting diodes (WOLEDs) with a simplified device configuration of ITO/4P-NPD or NPB/CBP:FPtXND/TPBI/LiF/Al or ITO/4P-NPD /4P-NPD:FPtXND/TPBI/LiF/Al.

A series of polyfluorene (PF) electrolytes bearing Br−, BF₄ −, or PF₆ − counterions were synthesized and characterized. 2,1,3-benzoselenadiazole moieties were incorporated into polymer main chains to produce single-component white lightemitting polymers. The thermal stability of Br-containing ionic PF was decreased because of the Hofmann elimination occurred at higher temperature. By replacing Br− with BF₄ − or PF₆ − counterions, the thermal stability of polymers was significantly improved. The emission intensity around 550 nm was decreased for ionic polyelectrolytes. The optimized spin-coated light-emitting electrochemical cell (LEC) with the configuration of ITO/PEDOT/polymer/Ag showed a maximum luminescence efficiency of 1.56 lm/W at a low operation bias of 3 V. The single-component LEC device exhibited pure white light emission with CIE’1931 coordinates approaching (0.33, 0.33) and high color rendering index (CRI < 85), referring to its potential use in solid-state-lighting application.

The far-field optical distribution characteristics of a planar white organic light-emitting diode (WOLED) source with 10x10mm² emissive area were experimentally investigated and compared to that of a near point-source white light-emitting diode (WLED) as control by using an automatic 2-axis optical measuring system in hemi-spherical space. WOLED has become a potential planar lighting source due to its single device structure consisted of multiple organic layers sandwiched by cathode and anode electrodes on glass substrate. The far-field optical distribution profiles and characteristics of a planar lighting source are crucial for optical design work in specific application. The far-field optical distribution characteristics of a planar WOLED source is expected to be unique and different compared to that of a near point source WLED. Our experimental result indicates that the far-field optical distribution function measured from near point-source WLED is close to that predicted by an ideal Lambertian source. The far-field optical distribution function measured from the planar WOLED source with 10x10 mm² emissive area reveals slightly different characteristics around normal direction from that of the near point-source WLED.

Inverted organic light-emitting diodes (IOLEDs) have drawn considerable attention for use in active-matrix OLED (AMOLED) displays because of their easy integration with n-channel metal-oxide-based thin film transistors (TFTs). The most crucial issue for IOLEDs is the poor electron injection caused by the bottom cathode. According to previous reports, the turn-on voltages of FIrpic-based IOLEDs are within a range from 4 to 8 V. In this study, we focus on developing bottom-emission IOLEDs with low operating voltages through the use of adequate-charge injection materials. We successfully demonstrate a turn-on voltage as low as 3.7 V for blue phosphorescent IOLEDs. The effective electron injection layers (EIL) were constructed by combining an ultrathin aluminum layer, an alkali metal oxide layer and an organic layer doped with alkali metal oxide, allowing for the effective adjustment of the carrier balance in IOLEDs. The peak efficiencies of the IOLEDs reached 15.6%, 31.8 cd/A and 23.4 lm/W. An external nanocomposite scattering layer was used to further improve light extraction efficiency. The IOLEDs equipped with the SiO2 nanocomposite scattering layer respectively provided performance improvements of 1.3 and 1.5 times that of pristine blue phosphorescent IOLEDs at practical luminance levels of 100 cd/m² and 1000 cd/m². Through sophisticated EIL and external light-extraction structures, we obtained blue phosphorescent IOLEDs with satisfactory efficiency and low operation voltages, thereby demonstrating the great potential of nanocomposite film for application in IOLEDs.

A series of novel thieno[3,2-c]pyridine-based RGBY phosphorescent Ir complexes have been synthesized and characterized. Solution-processable double-layered OLEDs fabricated with theses materials as the light-emitting layer exhibit high efficiencies. The monochromatic large-area of 40 x 83 mm² Yellow and Green OLEDs have also been demonstrated.

We study exciton-induced degradation of various organic/metal interfaces in organic optoelectronic devices. The results show that organic/metal interfaces are susceptible to irradiation in general, resulting in a deterioration in charge transport across the interfaces. We find that organic/metal interfaces containing the same organic material but different metals degrade quite differently, where interfaces with metals of high work function are more susceptible to exciton-induced degradation than those with metals of low work function. The results suggest a clear correlation between excitoninduced degradation of organic/metal interfaces and energy barrier for electron injection at organic/metal interfaces. Furthermore, the fact that the use of interfacial layers, which usually contain alkali metals of extremely low work function, can greatly improve organic/metal interfacial photo-stability is also, to a large extent, consistent with such correlation. The reason behind such correlation may stem from the difference in the strength of organic-metal bonds in organometallic compounds formed at different organic/metal interfaces and/or the difference in band bending of organic materials in the vicinity of organic/metal interfaces due to the use of metals of different work functions at the interfaces.

Highly efficient state of the art organic light-emitting diodes (OLED) comprise thin emitting layers with thicknesses in the order of 10 nm. The spatial distribution of the photon generation rate, i.e. the profile of the emission zone, inside these layers is of interest for both device efficiency analysis and characterization of charge recombination processes. It can be accessed experimentally by reverse simulation of far-field emission pattern measurements. Such a far-field pattern is the sum of individual emission patterns associated with the corresponding positions inside the active layer. Based on rigorous electromagnetic theory the relation between far-field pattern and emission zone is modeled as a linear problem. This enables a mathematical analysis to be applied to the cases of single and double emitting layers in the OLED stack as well as to pattern measurements in air or inside the substrate. From the results, guidelines for optimum emitter – cathode separation and for selecting the best experimental approach are obtained. Limits for the maximum spatial resolution can be derived.

Computational structure enumeration, analysis using an automated simulation workflow and filtering of large chemical structure libraries to identify lead systems, has become a central paradigm in drug discovery research. Transferring this paradigm to challenges in materials science is now possible due to advances in the speed of computational resources and the efficiency and stability of chemical simulation packages. State-of-the-art software tools that have been developed for drug discovery can be applied to efficiently explore the chemical design space to identify solutions for problems such as organic light-emitting diode material components. In this work, virtual screening for OLED materials based on intrinsic quantum mechanical properties is illustrated. Also, a new approach to more reliably identify candidate systems is introduced that is based on the chemical reaction energetics of defect pathways for OLED materials.

We present high efficiency orange emitting OLEDs with low driving voltage and low roll-off of efficiency using an exciplex forming co-host by (1) co-doping of green and red emitting phosphorescence dyes in the host and (2) red and green phosphorescent dyes doped in the host as separate red and green emitting layers. The orange OLEDs achieved a low turn-on voltage of 2.4 V and high external quantum efficiencies (EQE) of 25.0% and 22.8%, respectively. Moreover, the OLEDs showed low roll-off of efficiency with an EQE of over 21% and 19.6% at 10,000 cd/m², respectively. The devices displayed good orange color with very little color shift with increasing luminance. The transient electroluminescence of the OLEDs indicated that both energy transfer and direct charge trapping took place in the devices.

We study the correlation between the shift in recombination zone and the efficiency roll-off in typical PHOLEDs. To probe the shift in recombination zone, electroluminescence spectra of devices with various architectures at different current densities are studied. Results show that high efficiency at low current density mostly originates from the interfacial emission at the EML/ETL interface due to the formation of host excitons followed by the subsequent energy transfer to the guests. Furthermore, increase in the current density shifts the recombination zone from the EML/ETL interface towards the HTL/EML interface where the device emission is the result of direct charge trapping on the guest sites. The results suggest that the shift in recombination zone and subsequent change in emission mechanism play a main role on the efficiency roll-off.

In this work, admittance analysis of organic light emitting diode (OLED) (anode/active layer/cathode) was performed at room temperature within the frequency range of 1 kHz-1MHz to find out transport properties of both injected carriers from each side. Moreover, by proper chosen metals, electron or hole only OLED devices were prepared and the measurement was resumed to identify the governed transport path of injected carrier. Mobility of injected carriers followed the Poole-Frenkel type conduction mechanism and distinguished in the frequency range due to the difference of transit times in admittance measurement. Beginning of light output and onset of negative capacitance took place at the turn-on voltage (or flat band voltage), 1.8 V, which was the difference of energy band gap of polymer and two barrier offsets between metals and polymer. The proposed analytical model for admittance, derived for the frequency dependent space charge limited behavior leading negative capacitance issues, was applied on the measured data for the present OLED device.