This PDF file contains the front matter associated with SPIE Proceedings Volume 8476, including the Title Page, Copyright Information, Table of Contents, and the Conference Committee Listing.

We developed high-efficiency multi-photon emission (MPE) blue phosphorescent OLEDs with external quantum efficiency exceeding 40% at 100 cd m^–2. In these MPE devices, we used a blue phosphorescent emitter, FIrpic and pyridine-containing electron-transporters, 3,5,3’’,5’’-tetra-3-pyridyl-[1,1’;3’,1’]terphenyl (B3PyPB) and bis-4,6-(3,5- dipyridylphenyl)-2-methylpyrimidine derivatives (B3PyMPM, B4PyMPM). We also used a well-known electrontransporter, 2,9-dimethyl-4,7-diphenylphenanthroline (BCP) for comparison. We used a combination of TAPC/MoO₃/Al/Liq layers as the charge-generation layer unit. An optimized MPE device showed an extremely high current efficiency of over 90 cd A^–1 and a high power efficiency of over 40 lm W^–1 at 100 cd m^–2 without any outcoupling enhancement.

Newly prepared water-soluble iridium phosphorescent complexes, trans-[Ir(ppy)(PAr₃)₂(H)L]^0,+ (ppy = bidentate 2-phenylpyridinato anionic ligand; L= Cl (1), CO (2), CN- (3); H being trans to the nitrogen of ppy ligand; PAr₃ (TPPTS) = P(m-C₆H₄SO₃Na)₃), have been synthesized and characterized. Those complexes containing water-soluble phosphine ligands can emit any color region as altering cyclometalated ligands in aqueous media with high quantum efficiencies. Even though these water-soluble phosphorescent iridium complexes can be the sensing probe for toxic CO gas and CN anion, they will be capable of promising materials in the solution processible OLED applications.

Efficient and stable high energy organic light emitting devices (OLEDs) are a vital component of new generation general illumination solutions. However, large charge imbalances in the emissive layer of OLEDs lead to charge accumulation and subsequent side reactions which lowers the device efficiency and dramatically shortens operational lifetime. Radical changes in the way emitter materials are designed are needed to address this problem. Conventional approaches have only focused on color tuning; however, multi-functional emitter materials are needed to assist the transport of charge in the emissive layer. We have designed new organometallic iridium phosphorescent materials with bipolar charge transport properties to be used in high energy OLEDs and white light configurations. Theoretical data presented here indicates that these new emitter complexes would improve charge transport in the emissive layer.

We study the photo-stability of various organic/metal contacts under monochromatic illumination. The results show that the organic/metal contacts are susceptible to irradiation, leading to deteriorations in both charge injection (i.e. from the metal to the organic layer) and charge extraction (i.e. from the organic layer to the metal). As a result, the photo-stability of these organic/metal contacts plays an important role in the stability of organic light-emitting devices (OLEDs), where the photo-degradation is caused by the irradiation of device own electroluminescence (EL), and organic photodetectors (OPDs), where exposure to light is obviously a more relevant issue. It is also found that interfacial layers such as cesium carbonate (Cs₂CO₃) and lithium acetylacetonate (Liacac) can greatly improve the photo-stability of the organic/metal contacts, and thus improve the stability of organic optoelectronic devices such as OLEDs and OPDs.

The development of high performance organic light emitting diodes (OLEDs) for display and lighting applications has attracted considerable research interest from both academia and industry. In this work, the designs of simplified phosphorescent OLEDs with exceptionally high efficiency are discussed. It is found that discrete blocking layers and a double emission zone are unnecessary to achieve high efficiency in optimized phosphorescent OLEDs. Due to the elimination of these redundant layers, the device structure can be highly simplified. It is also shown that single-layer, two organic component devices are feasible with state-of-the-art efficiency.

The conformations and aggregated structures, such as molecular orientations, of organic molecules in organic light-emitting diodes (OLEDs) are considered to be closely related to the performance of OLEDs. Therefore, their clarification is of great importance in understanding device performance; however, the structures have not been fully analyzed because the organic molecules in OLEDs are often in amorphous states, and conventional methods for structure analysis, such as diffraction methods, do not provide sufficient information. In this study, we have attempted the analysis of molecular orientations of OLED materials by solid-state NMR, which is useful for structure analysis even for amorphous solids.

We reported a couple of methods to improve electron injection from the ITO electrode, thereby to fabricate efficient inverted bottom emission organic light emitting diodes (IBOLEDs). The first method is to use an n-doped electron transporting layer (ETL) as the electron injection layer. Electron only device characteristics and UPS measurements confirmed that B3PYMPM homo-junction has the lowest injection barrier at the interface among three different ETLs, resulting in the highest maximum EQE of 19.8% at low voltage in IBOLEDs. The energy barrier between n-ETL and ETL is one of the most important factors for high performance inverted OLEDs. The second method is to use an organic p-n junction as an electron injection layer, where the p-n junction generated electrons and holes under reverse bias, which corresponds to the forward bias in the OLEDs. The organic p-n junction composed of a p-CuPc/n-Bphen layer shows almost the same electron injection characteristics for the cathodes with different work functions whereas the injection characteristics of the n-Bphen EIL significantly depend on the work function of the cathode. These facts indicate that the organic p-n junction can be efficiently applied as an electron injection layer for high performance flexible organic electronics, regardless of the electrodes.

Energy transfer plays a key role in various applications of organic semiconductors such as electroluminescence, photovoltaics, and sensors. We have carried out a study combining transient and continuous wave (CW) optical spectroscopy with modeling. The fluorescence spectra and dynamics of a functionalized pentacene doped into a fluorescent host (Alq₃) were measured and simulated by a Monte Carlo model incorporating distributed dopants and exciton migration. For nonluminescent materials, transient absorption spectroscopy provides insight into excitation migration. Singlet diffusion rates in C60 were determined by probing delayed charge transfer to ZnPc in films with a layered nanostructure.

We report highly efficient blue polymer light-emitting diodes (PLEDs) achieved by introducing two nanoscale interfacial layer, made of poly(fluorine-co-triphrnylamine) [PFO-TPA] and cesium carbonate (Cs₂CO₃), between (1) the PEDOT:PSS and blue poly[9,9-diarylfluorene-co-2,5-Bisphenyl-1,3,4- oxadiazole] (P1)and (2) the aluminum cathode and the P1 emitter, individually. PFO-TPA with highest occupied molecular orbital level (-5.36 eV) lies between those of PEDOT:PSS (~5.0 ~ 5.2 eV) and P1 emitter (~5.54 eV), forming a stepwise energy ladder to facilitate the hole injection. For Cs₂CO₃, firstly, it enhances the injection of electrons by providing an lower electron injection barrier. Secondly, applied Cs₂CO₃ buffer decreases the PL intensity slowly down to ~96 % of the pristine P1 film, located at 422 nm, is less efficiency quenched than the Calcium (Ca). Therefore the overall electron injection attributed by Cs₂CO₃ buffer is higher. Thirdly, the device with Cs₂CO₃ buffer did not show the low-energy emission band originated from the fluorenone defects which are often introduced by Ca, thus stabilized blue emission from devices with high brightness can be demonstrated. Based on the hole-transporting PFO-TPA and the Cs₂CO₃/Al cathode, we obtained device efficiency and brightness as high as 13.99 cd A^-1 and 35054 cd m^-2, which is an improvement by two orders of magnitude higher over devices using Ca/Al as cathode and without hole-transporting PFO-TPA.

Triplet harvesting is a candidate technology for highly efficient and long-life white OLEDs, where green or red phosphorescent emitters are activated by the triplet-excitons diffused from blue fluorescent emitters. We examined two oxadiazole-based electron transport materials with different horizontal molecular orientation as a triplet-exciton diffusion layer (TDL) in triplet-harvesting OLEDs. The device characteristics and the transient electroluminescent analyses of the red phosphorescent emitter showed that the triplet-exciton diffusion was more effective in the highly oriented TDL. The results are ascribed to the strong orbital overlap between the oriented molecules, which provides rapid electron exchange (Dexter energy transfer) in the TDL.

We demonstrated a 42% luminance enhancement by attaching MLF (Micro Lens Film) on the bottom emitting OLED. Higher density of MLF extracted more substrate mode to air. We also investigated the compatibility of MLF and Circular Polarizer (CP) on the bottom emitting OLED. It is found that the efficiency of bottom emitting OLED with MLF and CP decreases comparing to the reference OLED device, which has CP alone. Simulation shows that large portion of light is reflected back into CP at the surface of MLF and air. Back reflected light from MLF is absorbed in CP layer. We have also shown that OLED blur image be enhanced by reducing substrate thickness.

Polymer composite electrodes based on silver nanowires or carbon nanotubes have been prepared with transparency and surface conductivity approaching those of ITO/glass and better than ITO/PET. The conductive surface has an average roughness less than 10 nm, better than ITO/glass. Depending on the polymer matrix selected, the composite electrodes can be made rigid, flexible like polycarbonate, or stretchable like a rubber. Various polymer light emitting diodes,light emitting electrochemical cells and polymer solar cells have been fabricated using the composite electrode as anode, exhibiting electroluminescent efficiencies generally higher than control devices fabricated on ITO/glass. These polymer light emitting devices are all highly flexible and can be bent to less than 3 mm radius without loss of performance. With further modification of the composite electrodes, we have also demonstrated stretchable OLEDs wherein the emissive area can be elongated by as much as 50%.

In this work, we demonstrate fully uniform blue fluorescence graphene anode OLEDs, which have an emission area of 10×7 mm². Catalytically grown multilayered graphene films have been used as the anode material. In order to compensate the current drop, which is due to the graphene’s electrical resistance, we have furnished metal bus lines on the support. Processing and optical issues involved in graphene anode OLED fabrications are presented. The fabricated OLEDs with graphene anode showed comparable performances to that of ITO anode OLEDs. Our works shows that metal bus furnished graphene anode can be extended into large area OLED lighting applications in which flexibility and transparency is required.

We fabricated the graphene based PLEDs that had the structure of glass / single layer graphene with Ag auxiliary electrode (anode) / PEDOT:PSS (HITL) / SPG-01T(Green polymer lighting material from Merck, EML) / Ca (EIL) / Al (Cathode). Single layer graphene was synthesized on copper foil by thermal CVD process, and then transferred to glass substrate by PMMA stamp. Formation of single layer graphene was confirmed from AFM, Raman spectroscopy, and UV-vis spectroscopy measurements. Graphene film was treated through a shadow mask for 15 minutes in UV ozone chamber to obtain anode pattern. After that, the patterned graphene layer was exposed to UV ozone to control its work function, which was found to be increased by 0.18eV and 0.27eV after 2.5 minutes and 5 minutes treatment, respectively. On the graphene layer, PEDOT:PSS and SPG-01T were consecutively spin-coated and annealed in the globe box. Ca and Al metal layer was deposited by thermal evaporation. Our graphene based PLEDs had the current efficiency of 9.73 cd/A and the power efficiency of 5.51 lm/W while our reference device with ITO anode showed the efficiencies of 12.5 cd/A and 8.01 lm/W.

Organic electronic devices like organic thin film transistors with micron or even sub-micron sized features can be fabricated at high throughput by fast printing methods combined with high resolution laser patterning. In addition, such an approach is of interest for applications with lower requirements in resolution, such as OLEDs or OPV. Due to its high flexibility and adaptability to almost any material or material system, laser processing is a perfect tool for the production of organic electronics. In all the applications above, it is of severe importance not to cause damage to adjacent material or layers by laser radiation. For transparent conductive layers laser-induced damage can lead to changes in conductivity, transparency or material composition (e.g. oxidation). Therefore, a comprehensive study was performed to investigate the influence of laser radiation below ablation threshold on material properties of transparent conducting layers (e.g. ITO, PEDOT/PSS). Samples were irradiated by a large range of wavelengths, reaching from the deep UV (193 nm) up to near IR (1064 nm). To identify changes in material properties the samples were characterized by microscopic methods like high resolution laser scanning microscopy and conductive atomic force microscopy. Also spectroscopic methods like UV/VIS/NIR absorption spectroscopy as well as X-ray photoelectron spectroscopy were used in order to determine changes in conductivity and material composition.

We report the demonstration of low threshold organic lasers whose nanostructured resonators are fabricated by UV nanoimprint lithography. We compare the nanoimprinted resonators with their master stamp nanostructures, and demonstrate lasers based on the conjugated polymer poly(2,5-Bis(2',5'-Bis(2"-ethylhexlyoxy))-p-phenylenevinylene), with thresholds of ~1 kW/cm² and below, which brings them into the regime where they can be optically pumped by a pulsed light-emitting diode.

Lasing action in electrically pumped organic laser device is demonstrated. A DCM laser dye doped Alq film serves as the active layer. High reflective and low loss electrical contacts are used to form a high quality factor coupled microcavity. Single longitudinal cavity mode is obtained at 618 nm with a threshold current density of 612 mAcm^-2 under room temperature continuous wave operation.

In this work, we present a novel way in fabricating a metal substrate with nanometer scale in surface roughness (R_a < 1 nm) using a surface roughness transfer method without any polishing or planarization process. Ag film (8 inch, R_a = 0.57 nm) and an INVAR (Invariable alloy) one (20 cm × 20 cm, R_a = 1.40 nm) were demonstrated. The INVAR film was used as a substrate for fabricating organic light emitting diodes (OLED) and organic photovoltaic (OPV). The optical and electrical characteristics of OLEDs and OPVs using the INVAR were comparable to those using a conventional ITO glass substrate.

The emission pattern of organic light-emitting diodes (OLEDs) is usually close to Lambertian. This paper explores the factors controlling the angular dependence of the emission from OLEDs. In particular it considers the question of how far from Lambertian can the emission of an OLED be? We have examined how wavelength-scale microstructure can modify the pattern of light emission from OLEDs. We demonstrate OLEDs in which emission is strongly directed towards, or away from, the forward direction. We consider the relative importance of scattering of waveguide modes, surface plasmons and microcavity effects in the strongly modified emission patterns which we observe.

Insertion of high work function (WF) transition metal oxide (TMO) layers between the anode and the hole transport layer is established to substantially enhance the performance of organic light emitting diodes (OLED). The high WF of transition metal oxide layer has been demonstrated to be the most crucial for the enhancement. The WF of a TMO layer decreases substantially with air exposure, and noticeably by the ambient even inside a low vacuum system. In the present work we discuss various methods to protect and recover the high WF after a TMO thin film has been exposed to air. We report covering a thin organic layer on top of MoO_x to protect the high work function. We found that a thin layer of 1-2 nm organic layer was sufficient to protect the work function of MoO_x thin film underneath. We further report methods to recover already decreased TMO WF due to air exposure. We performed oxygen plasma cleaning of air exposed MoO_x film and found out that oxygen plasma could substantially recover the WF of as deposited MoO_x film. We also performed annealing of air exposed MoO_x film inside an ultra high vacuum system and observed a thin layer of oxygenrich adsorbate layer, which desorbed upon annealing that in turn substantially recovered the MoO_x WF. We discuss the vacuum annealing and the effect of resulting surface on the interface energy level alignment.

Photoluminescence (PL) spectroscopy has been performed in-situ on iridium(III) ionic transition metal complex (iTMC)- based sandwich-type light-emitting electrochemical cells (LECs) during device operation and after switch-off. It is demonstrated that driving the device leads to a considerable decrease of the PL intensity of the active layer. Two different time regimes for this decrease have been identified. The first one is characterized by a complete recovery of the PL after the device is turned off corroborating the existence of dynamically formed doped regions also in iTMC-based LECs. In the second regime the PL does not completely recover which is attributed to a permanent degradation of the active layer that is the main source for the low lifetime of the devices. Additionally, it is demonstrated how to externally stabilize the dynamic configuration leading to a half lifetime in excess of 1000 hours at simultaneous high brightness of more than 1000 cd/m² and fast turn-on of less than one second.

Numerous medical research studies reveal intense white or blue light to drastically suppress at night the secretion of melatonin (MLT), a protective oncostatic hormone. Lighting devices with lower color-temperature (CT) possess lesser MLT suppression effect based on the same luminance, explaining why physicians have long been calling for the development of lighting sources with low CT or free from blue emission for use at night to safeguard human health. We will demonstrate in the presentation the fabrication of OLED devices with very-low CT, especially those with CT much lower than that of incandescent bulbs (2500K) or even candles (2000K). Without any light extraction method, OLEDs with an around 1800K CT are easily obtainable with an efficacy of 30 lm/W at 1,000 nits. To also ensure high color-rendering to provide visual comfort, low CT OLEDs composing long wavelength dominant 5-spectrum emission have been fabricated. While keeping the color-rendering index as high as 85 and CT as low as 2100K, the resulting efficacy can also be much greater than that of incandescent bulbs (15 lm/W), proving these low CT OLED devices to be also capable of being energy-saving and high quality. The color-temperature can be further decreased to 1700K or lower upon removing the undesired short wavelength emission but on the cost of losing some color rendering index. It is hoped that the devised energy-saving, high quality low CT OLED could properly echo the call for a physiologically-friendly illumination for night, and more attention could be drawn to the development of MLT suppression-less non-white light.

Organic lighting-emitting diode (OLED) is one of the most attractive technologies for next generation light source due to its merits of good color rendering performance, diffuse area light source and high luminance efficiency. Despite its strong potential as a large-area planner light source, light emitting area of one OLED lighting panel has been limited because of high sheet resistance of transparent conductive electrodes and high risk of electrically short defects. In this paper, we demonstrate a novel design for large-area OLED lighting panels with low electrode resistance and 100% short reduction to achieve high brightness uniformity with low power efficiency loss and high production yield at the same time. In addition, total light output of OLED lighting panels can be further enhanced by applying an internal extraction layer between transparent electrodes and glass substrate.

Organic Light Emitting Diodes (OLEDs) provide various attractive features for next generation illumination systems, including high efficiency, low power, thin and flexible form factor. In this work, we incorporated phosphorescent emitters and demonstrated highly efficient white phosphorescent OLED (PHOLED) devices on flexible plastic substrates. The 0.94 cm² small-area device has total thickness of approximately 0.25 mm and achieved 63 lm/W at 1,000 cd/m² with CRI = 85 and CCT = 2920 K. We further designed and fabricated a 15 cm x 15 cm large-area flexible white OLED lighting panels, finished with a hybrid single-layer ultra-low permeability single layer barrier (SLB) encapsulation film. The flexible panel has an active area of 116.4 cm², and achieved a power efficacy of 47 lm/W at 1,000 cd/m² with CRI = 83 and CCT = 3470 K. The efficacy of the panel at 3,000 cd/m² is 43 lm/W. The large-area flexible PHOLED lighting panel is to bring out enormous possibilities to the future general lighting applications.

Delayed electroluminescence (Delayed EL) measurements are used to investigate the emission mechanism in typical Phosphorescent Organic Light Emitting Devices (PHOLEDs). In this work, emission mechanism of PHOLED based on CBP (4,4'-bis(carbazol-9-yl)biphenyl : Ir(ppy)₃ (Tris(2-phenylpyridine)iridium(III)) host:guest system is studied. The technique is used to understand whether the EL emission arises from charge recombination directly on guest sites or from recombination on host material followed by host to guest energy transfer. The results show that the emission mechanism changes with the emission layer (EML) thickness. In the case of devices with a thick EML, strong host triplet-triplet annihilation (TTA) is observed, suggesting the presence of significant energy transfer from host to the guest. For the case of devices with thin EML, on the other hand, host TTA is insignificant, suggesting that direct charge trapping on the guest is the main emission mechanism. The results also show that the thickness of the hole transport layer (HTL) has negligible effect on the emission mechanism of PHOLED, showing that the emission mechanism mainly depends on the EML.

A modelling approach for carrier transport in a Gaussin density of states is presented which takes into account that the energetic distribution of carriers moving via Miller-Abrahams rates is affected by an electric field. This reorganisation of the energetic carrier distribution can be described by virtual carrier heating to an effective temperature. We show that combining this approach with an existing percolation model reproduces the field dependence found in computer studies in literature for uncorrelated Gaussian disorder. Comparing to our experimental results, we also demonstrate that the parameterizations from these publications do not hold at low temperatures. We produced samples of 4,4′,4″-tris-(2-methylphenyl phenylamino)triphenylamine (m-MTDATA) doped into N,N'- diphenyl-N,N'-bis(1-naphthylphenyl)-1,1'-biphenyl-4,4'-diamine (NPB) in the ratio 1:1 with four different thicknesses from 50 nm to 400 nm and measured the IV curves in a temperature range from T=77 K to 346 K. We successfully demonstrate a unified simulation of the samples’ IV characteristics over the entire temperature range under the assumption of carrier heating, which is not possible with published models for correlated and uncorrelated Gaussian disorder.

Organic and hybrid organic / inorganic semiconductor heterostructures offer great potential as key technology for cost-efficient electro-photonic devices. To exploit their full potential, fundamental understanding of charge carrier injection is essential. Therefore we use current-luminance-voltage (I-L-V) and capacitance-voltage (C-V) measurements to analyze the injection characteristics of monochrome OLED test structures and hybrid organic / inorganic (HOI) pentacene / n-GaN and Alq₃ / n-GaN heterostructures processed by organic vapor phase deposition (OVPD) and metal organic chemical vapor deposition (MOCVD), respectively. In a first step, we fundamentally analyze the specific C-V characteristics of OLED test structures. The multilayer devices show additional features in the C-V profile as compared to the bilayer OLED investigated by Brütting et al.^1,2. We attribute this behavior to the additional organic / organic interfaces and the resulting energetic barriers in multilayer devices. In addition, we compared the C-V measurements of pristine and degraded OLED test structures. Here we conclude that a deterioration of hole injection in degraded devices is dominant, whereas electron injection remains largely unaffected. Furthermore, in pristine and degraded OLED, increased temperatures generally lead to improved charge injection as well as a reduced impact of the additional barriers in multilayer stacks. By analyzing I-V and C-V measurements of HOI heterostructures, we find ambipolar currents in pentacene-based diodes with electrons from n-GaN being injected at lower bias than the onset of hole injection from the gold anode contacts. Generally, I-V measurements of both types of HOI heterostructures show an onset of charge injection at very low bias voltage. Accordingly, n-GaN offers superior electron injection characteristics recommending n-GaN as cathode contact e.g. in fully transparent OLED microdisplays.

Excessive charge carrier densities in the emission layer of organic light-emitting diodes (OLEDs) can lead to significant quenching by triplet-polaron-annihilation [1] or field-induced quenching [2]. Thus, to increase the efficiency of OLEDs further, a technique for the reliable determination of charge carrier densities in OLEDs is most desirable. Time-resolved spectroscopy is a powerful tool to investigate electronic and excitonic transfer processes [3]. By application of a voltage pulse to a phosphorescent state-of-the-art OLED we find a transient overshoot after voltage turn-off. This has primarily been found in phosphorescent OLEDs and has typically been attributed to delayed recombination of trapped charge carriers [4-7]. In this contribution we investigate charge carrier accumulation within the emission layer (EML) and provide a method to quantify the density of stored electrons.

Accurate optical modeling of OLED device performance is beneficial to OLED manufacturing because as materials and architectures are modified, experimental effort and resources are saved in the search for optimal structures. The success of such modeling depends crucially on model inputs, which include, along with layer thicknesses and optical constants, internal emission characteristics such as the internal emission spectrum (IES) of the emitter and the location and profile of emission in the emissive layer (EML). This presentation will describe two methods we have used to extract the internal emission characteristics of our printed bottom emitting OLEDs. The first method, which we devised and implemented with assumptions specific to our devices, is a simpler one for both modeling and data collection: we collected spectra at normal viewing angle for a series of devices with different architectures, and extracted a normalized IES common to all these devices. We will show how an emission location was obtained from this method with some simple model assumptions. In the more rigorous second method - one presented by van Mensfoort et al 1 - internal emission characteristics were extracted independently for each device: spectra at multiple angles were collected, which allowed the extraction of an individual IES and emission profile. We will compare the findings of the two methods and assess the validity of the assumptions used in the first method.

The solution/evaporation hybrid processed organic light emitting devices composed of newly developed host material CzDBS, green PG-02 dopant, and orange PO-01-TB and PO-06 dopants are studied. Orange, green and two-peak white light emitting devices were fabricated by using spin coating of HIL, HTL and emission layers followed by thermal evaporation of ETL and cathode. The orange devices achieved efficacies of 26.9 cd/A and 14.6 lm/W at the brightness of 1538 nits. The green devices, on the other hand, achieved efficacies of 31.3 cd/A and 19.7 lm/W at the brightness of 1590 nits. The two-peak white devices, composed of blue FIrpic and orange PO-01-TB, achieved efficacies of 36.9 cd/A and 18.4 lm/W at the brightness of 1150 nits.

Being introduced more than 20 years ago, OLEDs have seen a strong push in particular in the last two years, mostly driven by key players in the flat panel display industry. The majority of OLEDs manufactured today are deposited by vacuum thermal evaporation (VTE). Whilst this approach enables the making of high-performance devices scaling up of this approach has met new challenges when substrate dimensions are exceeding the "proof-of-principle" dimensions of pilot lines. Total production costs are increasingly moving into the focus of consideration. With Organic Vapor Phase Deposition (OVPD), AIXTRON has commercialized the principle of utilizing inert carriergas for the transport and controlled condensation of small molecules. While the original concept had been proposed by Prof. Steven Forrest at Princeton University, AIXTRON added its expertise in scaling gas phase processes to make this technology applicable for high-throughput production. Combining the basic concept of OVPD with AIXTRON's comprehensive expertise in utilizing close coupled showerheads and the underlying scaling rules, the disruptive approach offers a number of significant advantages: 1) decoupling of evaporation source and deposition system: additional freedom and independent optimization of source design and deposition area; 2) Utilization of carrier-gas for a more efficient evaporation, potentially increasing process windows; 3) Close-coupled showerhead approach realizes high material utilization with homogeneity; 4) Control of deposition rates by carrier-gas flow instead of the evaporation temperature enables precise rates control, co-deposition of various materials at changing rates. This paper will discuss the most significant differences compared to VTE and explain how the approach addresses requirements for efficient scaling as well as enabling advanced structure designs.

We report the rate limiting step of charge generation in the charge generation units (CGUs) composed of a p-HTL, HATCN and n-doped electron transporting layer (n-ETL) where TAPC was used as the HTL. Energy level alignment determined by the capacitance-voltage (C-V) measurements and the current density-voltage characteristics of the structure clearly showed that the electron injection at the HATCN/n-ETL junction limits the charge generation in the CGUs rather than charge generation itself at the p-HTL/HATCN junction. Consequently, the CGUs with 30 mol% Rb₂CO₃ doped BPhen formed with the HATCN layer generates charges very efficiently and the excess voltage required to generate the current density of ±10 mA/cm² was around 0.17 V, which is extremely small compared with the literature values reported up to now.

PCTrz, a new bipolar host material containing a phenoxy-carbazole separated from a biscarbazolyl-triazine by a non-conjugated ether bond is presented. Computational calculations demonstrated the separation of PCTrz into an oxidation and a reduction site. A phosphorescent OLED with PCTrz as host and FIrpic as blue emitter yielded high current efficiencies of up to 16.2 cd/A. Additionally two electron transporting host materials DBFTaz and DBFTazC, both containing 1,2,4-triazole moieies, were synthesized and characterized. The triazole moiety in DBFTaz was formed by a classical ring closure reaction between a N-benzoylbenzimidate and a hydrazine. For DBFTazC we used another synthetical pathway which involves subsequent coupling of a carbazole and a triazole moiety to a dibenzofuran core. Both triazoles posses high triplet energies of 2.95 eV for DBFTaz and 2.97 eV for DBFTazC, which make the compounds interesting as matrix materials for blue phosphorescent OLEDs.

Cs₂CO₃ is shown as a good electron injection material in organic electronic devices for its strong electron injection ability and being insensitive to the choice of metal cathode. Although it is hypothesized that the organic layer adjacent to the Cs₂CO₃ is crucial to realize efficient electron injection, little work is carried out to study the electron injection capability of cathode when Cs₂CO₃ contacts with different organic materials. Here a phenanthroline (Bphen) thin layer has been inserted at Alq₃/Cs₂CO₃ interface to improve electron injection, and the responding mechanism is also studied. When locating a 5 nm Bphen layer at Alq₃/Cs₂CO₃ interface, OLEDs performed much larger current. A photovoltaic experimental was conducted to study the build-in electrical field in OLEDs, which would give a hint for the work function change of cathode when Bphen interlayer was used; and the ultraviolet-visible absorption spectroscopy was also used to study the electronic structure change of Bphen when it contacts with Cs₂CO₃. Our study suggest that the cathode work function does not change obviously when Bphen interlayer is used, but much stronger charger transfer takes place between Bphen and Cs₂CO₃ than that between Alq₃ and Cs₂CO₃, so that a stronger dipole and a lower electron injection barrier can be expected playing a role at Bphen/Cs₂CO₃ interface.

Significant development has been made on phosphorescent organic light emitting diodes (PHOLEDs) over the past decade, which eventually resulted in the commercialization of widely distributed active-matrix organic light emitting diode displays for mobile phones. However, higher efficiency PHOLEDs are still needed to further reduce the cost and lower the power consumption for general lighting and LED backlight applications. In particular, red PHOLEDs currently have in general the lowest efficiencies among the three primary colors, due most likely to the energy-gap law. Therefore, a number of groups have of made use of various device configurations, including insertion of a carrier blocking or exciton confining layer, doping the transport layers, as well as employing multiple emissive zone structures to improve the device efficiency. However, these approaches are rather inconvenient for commercial applications. In this work, we have developed a simpler way to boost the performance of red PHOLEDs by incorporating an exciton harvesting green emitter, which transfers a large portion of the energy to the co-deposited red emitter. A high external quantum efficiency (EQE) of 20.6% was achieved, which is among the best performances for red PHOLEDs.

We demonstrated that an organic p–n junction was successfully adapted to inverted organic light emitting diodes (IOLEDs) as an electron injection layer (EIL). The organic p–n junction composed of a ReO₃ doped copper phthalocyanine (CuPc)/Rb₂CO₃ doped 4,7-diphenyl-1,10-phenanthroline (Bphen) layer showed very efficient charge generation under a reverse bias reaching to 100 mA/cm² at 0.3 V and efficient electron injection from indium tin oxide (ITO) when adopted in IOLEDs. Moreover, the organic p–n junction resulted in the same current density–voltage–luminance characteristics independent of the work function of the cathode, which is a valuable advantage for flexible displays.

Non-blocking Phosphorescent Organic Light Emitting Diode (NB-PHOLED) is a highly simplified device structure that has achieved record high device performance on chlorinated ITO[1], flexible substrates[2], also with Pt based phosphorescent dopants[3] and NB-PHOLED has significantly reduced efficiency roll-off[4]. The principle novel features of NB-PHOLED is the absence of blocking layer in the OLED stack, as well as the absence of organic hole injection layer, this allows for reduction of carrier accumulation in between organic layers and result in higher efficiencies.

For the lighting purpose, white organic light-emitting devices (OLEDs) need to be operated at a high current density to ensure an ample flux, which will lead the limited lifespan of the device. This situation could be improved through diversified light-extraction methods. In this study, transparent photoresist mixed with titanium oxide (TiO₂) nanoparticles of different sizes could be utilized to form an internal extraction structures between the indium-tin-oxide and glass substrate and thereby the out-coupling efficiency of white OLEDs could be significantly improved by this sophisticated device architecture engineering. The high refractive index of TiO₂ is essentially operative for increasing the refractive index of nanocomposite film and thus diminishing the total internal reflection between the interfaces. In addition, the nanoparticles served scattering function to multiply the ratio of the substrate and radiation modes. By employing nanocomposite substrate with mixed dual-sized nanoparticles, we obtained external quantum efficiencies of the white phosphorescent OLEDs that were about 1.6 times higher than that of the control device at the high luminescence of 10⁴ cd/m².

We proposed an internal nanostructure with a high reflective index planarization layer to solve the optical loss due to the reflective index mismatch between ITO and glass substrate. In our experiments, we found the electrical property of OLED device was significantly influenced by the internal nanostructures without planarization layer. Moreover, the internal extraction structure (IES) is not necessarily beneficial for light extraction. Therefore, we proposed a new substrate combine both internal and external extraction structure (EES) to extract trapping light. We successfully developed a high refractive index (N~1.7) planarization material with flat surface (RMS roughness < 2 nm), and improved about 70% device efficiency compared to traditional glass substrate.

We have made a sol-gel deposited gallium-doped zinc oxide (GZO) film as a transparent conductive anode in polymer light-emitting diode (PLED) applications. The GZO films were obtained by spin-coating GZO precursor solutions followed by consecutive thermal annealing in the air and in the hydrogen-rich atmosphere. The resistance of GZO film was reduced to ~100 Ω/□ after thermal annealing in the hydrogen environment. Its surface roughness was sufficiently low (1.159 nm RMS) for depositing other polymer layers. We have fabricated PLEDs with quartz substrate / solution-processed GZO electrode (anode) / PEDOT:PSS (HITL) / SPG-01T (Green polymer light-emitting material purchased from Merck, EML) / Ca (EIL) / Al (Cathode). The fabricated devices showed current efficiency of 3.06 cd/A and power efficiency of 1.25 lm/W at luminance of 1000 cd/m².

In this study, we demonstrate electrophosphorescent organic light-emitting diodes (PHOLEDs) with a simple structure and high efficiency, utilizing fac-tris(2-phenylpyridine)iridium(III) (Ir(ppy)₃) as a green phosphorescent emitter. The device structure (ITO/TAPC/TAPC:Ir(ppy)₃/TPBi:Ir(ppy)₃/TPBi /LiF/Al) was fabricated by the hole transporting layer of 1,1-bis((di-4-tolylamino)phenyl)cyclohexane (TAPC; T₁ = 2.87 eV) and the electron transporting layer of 2,2,2-(1,3,5-benzenetriyl)tris-[1-phenyl-1H-benzimidazole] (TPBI; T₁ = 2.74 eV) to assemble a double emitting zone without common host materials. The emitting region with a TAPC/TPBI bilayer interface was able to provide an effective energy transference of Ir(ppy)₃ (T₁ = 2.4 eV). Thus, the green PHOLED exhibited high current efficiency (70 cd/A at 100 cd/m²) and low roll-off in these devices.

In this study, a flexible photonic crystal laser was demonstrated with InGaAsP nano rods on a polydimethylsiloxane (PDMS) substrate. The InGaAsP nano-rods content 4 quantum wells which are designed for 1.55 μm communication wavelength. The lasing action was observed around 1550nm which is a band-edge emission at high-symmetry Γ-point of photonic crystals. One of advantages of the flexible laser is the fine-tuning of optical properties by manipulating its geometry. In this work, we observed the lasing wavelength can be controlled by increasing photonic crystal lattice extension. The lasing wavelength was linearly red-shift up to 6 nm as the lattice extension percentage increased to 2.2%. The wavelength tuning rate is approximately 2.69 nm for 1 % lattice extension. Those geometric fine-tuning properties indicate the flexible photonic crystal laser can be applied as a compact tunable light source in photonic crystal integrated circuits or biomedical sensors.

The top-emitting OLED has higher light efficiency comparing to the bottom-emitting OLED due to the high aperture ratio. In this paper, we have analyzed the optical characteristics of the encapsulation layer with the organic and inorganic multi-layer structure for top emitting OLED. The thickness of the layer structure is optimized to achieve high transmittance by the transfer matrix method. We also calculated the transmittance of organic/inorganic multilayer in terms of incident angle and wavelength. The transmittance of the multi-layers above 90% was achieved for whole incident angle in the visible range.

MicroSystems is able to provide systems for specialized large area processing based on plasma enhanced chemical vapor deposition (PECVD) and physical vapor deposition (PVD) technologies. The generation of barrier layers has become an important field in a variety of applications. Systems for generating ultra-barrier layers and achieved results are presented and discussed.

A major barrier to commercial adoption of organic light emitting diode (OLED) based devices is their often unacceptably fast rate of degradation. Typically, to estimate device lifetime, electrical parameters such as driving voltage and luminance are periodically measured while constant current is applied to the OLED. Due to the repetitive nature and long timescales involved in lifetime testing, the procedure is an ideal candidate for automation. An automated lifetimetesting system and accompanying software was developed to simultaneously drive multiple OLED devices and collect lifetime parameters while the entire system is under ultra-high vacuum conditions. The system is connected to a larger vacuum chamber so that devices can be synthesized and then analyzed in situ without exposure to atmosphere. The system was developed with the aim of facilitating rapid discovery and understanding of OLED degradation mechanisms.

The formation of the aggregate and excimer in light-emitting polyfluorenes during annealing at high temperatures was reduced by adding coil-like block segments through atom transfer radical polymerization (ATRP), initialized by 2- bromoisobutyrate end-capped PF macroinitiator using CuBr/N,N,N',N',N''-pentamethyldiethylenetriamine (PMDETA) catalyst system. The rod-like macroinitiator was synthesized by the Yamamoto-type coupling using a Ni(COD)₂ catalyst. The structure and physical properties were characterized by ¹H NMR, thermal analysis, GPC, photoluminescence, small angle X-ray scattering and transmission electron microscopy. The addition of the coil-like block segments to the rod-like block segment resulted in the microphase separation between the component blocks which decreased the effective conjugation length of the conjugated moieties. The photoluminescence spectra measured from the thin films of the block copolymers revealed that the coil-like endblocks, attached to the conjugated block segments, suppressed the excimer formation of the PF molecules during annealing at high temperature.

The thermal conductivity of the organic light-emitting material in a white organic light-emitting diode (WOLED) was precisely estimated by solving two-dimensional transient heat transfer equation and fitting experimental data. A WOLED usually operates in relatively high current mode to maintain higher brightness for lighting application. A practical solution for heat dissipation is crucial for properly applying WOLED in lighting application. Thermal conductivity of a material is a critical parameter for developing heat dissipation solution. A typical WOLED consists of several thin organic light-emitting layers with similar thermal characteristics sandwiched by anode and cathode. These organic layers can be regarded as a single organic light-emitting material for simplifying thermal analysis. The thermal characteristic of the organic light-emitting material can be represented by an effective or equivalent thermal conductivity in analytical model. The analytical model of temperature distribution was obtained from solving two-dimensional transient heat transfer equation with simplified bi-layer structure. The effective thermal conductivity of the thin-film organic light-emitting material can be precisely estimated by fitting analytical temperature distribution function to the experimental data. Our preliminary investigation indicates that the thermal conductivity of the organic light-emitting material is estimated between 0.28 and 0.29 w/m°C, similar to well-known organic compounds.

The main purposes of this study are replacing conventional hydro-thermal method by microwave heating using water as reaction medium to rapidly synthesize TiO₂.Titanium tetraisopropoxide (TTIP) was hydrolyzed in water. The solution is subsequently processed with microwave heating for crystal growth. The reaction time could be shortened into few minutes. Then we chose different acids as dispersion agents to prepare TiO₂ paste for investigating the effects of dispersion on the power conversion efficiency of dye-sensitized solar cells (DSCs). The photovoltaic performance of the microwave-assisted synthesized TiO₂ achieved power conversion efficiency of 6.31% under AM 1.5 G condition (100 mW/cm²). This PCE value is compatible with that of the devices made from commercial TiO₂.