This PDF file contains the front matter associated with SPIE Proceedings Volume 9183, including the Title Page, Copyright information, Table of Contents, Authors, and Conference Committee listing.

Functional bio-interlayer organic field - effect transistors (FBI-OFET), embedding streptavidin, avidin and neutravidin as bio-recognition element, have been studied to probe the electronic properties of protein complexes. The threshold voltage control has been achieved modifying the SiO₂ gate diaelectric surface by means of the deposition of an interlayer of bio-recognition elements. A threshold voltage shift with respect to the unmodified dielectric surface toward more negative potential values has been found for the three different proteins, in agreement with their isoelectric points. The relative responses in terms of source – drain current, mobility and threshold voltage upon exposure to biotin of the FBI-OFET devices have been compared for the three bio-recognition elements.

One example of organic electronics is the application of polymer based light emitting devices (PLEDs). PLEDs are very attractive for large area and fine-pixel displays, lighting and signage. The polymers are more amenable to solution processing by printing techniques which are favourable for low cost production in large areas. With phosphorescent emitters like Ir-complexes higher quantum efficiencies were obtained than with fluorescent systems, especially if multilayer stack systems with separated charge transport and emitting layers were applied in the case of small molecules. Polymers exhibit the ability to integrate all the active components like the hole-, electron-transport and phosphorescent molecules in only one layer. Here, the active components of a phosphorescent system – triplet emitter, hole- and electron transport molecules – can be linked as a side group to a polystyrene main chain. By varying the molecular structures of the side groups as well as the composition of the side chains with respect to the triplet emitter, hole- and electron transport structure, and by blending with suitable glass-forming, so-called small molecules, brightness, efficiency and lifetime of the produced OLEDs can be optimized. By choosing the triplet emitter, such as iridium complexes, different emission colors can be specially set. Different substituted triazine molecules were introduced as side chain into a polystyrene backbone and applied as electron transport material in PLED blend systems. The influence of alkyl chain lengths of the performance will be discussed. For an optimized blend system with a green emitting phosphorescent Ir-complex efficiencies of 60 cd/A and an lifetime improvement of 66.000 h @ 1000 cd/m² were achieved.

The mass market application of OLEDs is currently hindered because i) the materials are too expensive and contain rare metals such as iridium and ii) current processing techniques are elaborate and cannot easily be up-scaled. Solution processable Cu(I)-complexes promise to solve both problems with one blow: Copper is an abundant metal, which offers new opportunities to develop materials for OLEDs. Due to their structural diversity, Cu(I) emitters allow for the design of materials with tunable properties. Beside this, it is also possible to adjust solution properties and introduce functionalities for cross-linking. The new materials feature exciting photophysical properties such as PLQY values close to unity and a tunable emission. The emission decay times are in the range of common emitters or lower, which is expected to reduce efficiency roll-off at high driving voltages. Cu(I)-complexes often feature thermally-activated delayed fluorescence (TADF). As a consequence, they can make use of triplet and singlet excitons in a process called Singlet Harvesting, which paves the way for high efficiencies. Unlike Ir(III)-complexes such as Irppy₃, triplet-triplet annihilation does not occur when using Cu(I), even in very high doping concentrations. The feasibility of NHetPHOS-type Cu(I)-complexes is demonstrated as well as strategies that enable a smart crosslinking process, where the Cu(I) emitters themselves play an important role. In addition, high-brightness devices, which were operated at medium voltages, yielding 50.000 cd m^-2 are shown. In a showcase example, we recently presented a device with an external quantum efficiency greater than 20% with a solution processed Cu(I)-PyrPHOS-device without using outcoupling techniques.

To realize low-cost fabrication processes for high-performance OLED displays and lighting panels, the understanding of solution-processed films and devices is becoming more important nowadays. However, differences between vacuum- and solution-processed films have not been sufficiently discussed, and they are sometimes regarded as identical. In this presentation, we show and discuss the important differences between physical properties of vacuum-deposited and spin-coated films of small-molecule OLED materials, especially focusing on the differences in film densities and molecular orientation. Since they are fundamental factors affecting both electrical and optical properties of amorphous films used in OLEDs, we should consider their differences carefully when discussing device performances in detail.

Recent progress has shown that molecular orientation in vapor-deposited glasses can affect device performance. The deposition process can result in films where the molecular axis of the glass material is preferentially ordered to lie parallel to the plane of the substrate. Here, materials made within Dow’s Electronic Materials business showed enhanced performance when the orientation of the molecules, as measured by variable angle spectroscopic ellipsometry, was oriented in a more parallel fashion as compared to other materials. For one material, the anisotropic packing was observed in the as-deposited glass and was isotropic for solution-cast and annealed films. In addition, the density of an as-deposited N,N′-bis(naphthalene-1-yl)-N,N′-bis(phenyl)-2,2′-dimethylbenzidine (NPD) film was 0.8% greater than what was realized from slowly cooling the supercooled liquid. This enhanced density indicated that vapor-deposited molecules were packing more closely in addition to being anisotropic. Finally, upon heating the NPD film into the supercooled liquid state, both the density and anisotropic packing of the as-deposited glass was lost.

In organic light-emitting diodes (OLEDs), device degradation is one of the crucial problems to be solved. In this study, we have investigated material degradations in FIrpic-based phosphorescent OLEDs by solution nuclear magnetic resonance (NMR) spectroscopy. NMR experiments clearly indicate that about 18% of TPhDB molecules, which is used as an electron-transporting material, are decomposed during driving the devices. The decomposition of the TPhDB molecules is considered to be related to the device degradation. This study demonstrates that solution NMR spectroscopy is a useful tool to investigate an origin of device degradation of multi-layered OLEDs in terms of decomposition of organic molecules.

A feature of OLEDs that has to date received little attention is the prediction of the stability of the molecules involved in the electrical and optical processes. Here, we present computational results intended to aid in the development of stable systems. We identify degradation pathways and define new strategies to guide the synthesis of stable materials for OLED applications for both phosphorescent emitters and organic host materials. The chemical reactivity of these molecules in the active layers of the devices is further complicated by the fact that, during operation, they can be either oxidized or reduced (as they localize a hole or an electron) in addition to forming both singlet and triplet excitons.

Detailed photophysical studies are presented for Cu₂Cl₂(dppb)₂ and Ag₂Cl₂(dppb)₂. Both compounds show very effective thermally activated delayed fluorescence (TADF) at ambient temperature with an emission quantum yield of the Ag(I) complex of Φ_PL(300 K) = 93 %. This emission is blue shifted by 65 nm (2500 cm^-1) with respect to the emission of the Cu(I) complex, demonstrating a valuable strategy for engineering blue light emitters. Potentially, these materials are well suited for taking advantage of the singlet harvesting effect in an OLED device. Moreover, both compounds do not show effects of concentration quenching at high emitter concentration, a property which might be attractive for reducing the efficiency roll-off at higher current densities. Investigations down to T = 1.6 K show that spin-orbit coupling (SOC) is particularly weak. This is displayed in the very long emission decay times of the triplet states (T₁ states) of metal-toligand charge transfer (³MLCT) character, amounting to τ(Ag₂Cl₂(dppb)₂) = 1.1 ms and τ(Cu₂Cl₂(dppb)₂) = 2.2 ms. According to the TADF mechanism, which leads to the additional decay channel at ambient temperature via the S₁ state (of ¹MLCT character), an increase of the radiative rate by a factor of 70 and almost 500 for Ag₂Cl₂(dppb)₂ and Cu₂Cl₂(dppb)₂, respectively, is induced. This results in radiative rates at ambient temperature of k_r = 6.2 ∙ 10⁴ s^-1 (τ_r = 16 μs, Ag(I) complex) and 11.7 ∙ 10⁴ s^-1 (τ_r = 8.5 μs, Cu(I) complex). Simple approaches are presented that allow us to understand the weakness of SOC on the basis of results from DFT and TD-DFT calculations. Investigations of the emission decay properties down to T = 1.6 K further support the conclusions with respect to the SOC strength.

Organic light emitting diodes (OLEDs) show potential as the next generation solid state lighting technology. A major barrier to widespread adoption at this point is the efficiency droop that occurs for OLEDs at practical brightness (~ 5000 cd/m²) levels necessary for general lighting. We highlight recent progress in highly efficient OLEDs at high brightness, where improvements are made by managing excitons in these devices through rational device design. General design principles for monochrome OLEDs are discussed based on recent device architectures that have been successfully implemented. We expect that an improved understanding of exciton dynamics in OLEDs in combination with innovative device design will drive future development.

Pi-conjugated polymer light emitting devices have the potential to be the next generation of solid state lighting. In order to achieve this goal, a low cost, efficient and large area production process is essential. Polymer based light emitting devices are generally deposited using techniques based on solution processing e.g.: spin coating, ink jet printing. These techniques are not well suited for cost-effective, high throughput, large area mass production of these organic devices. Ultrasonic spray deposition however, is a deposition technique that is fast, efficient and roll to roll compatible which can be easily scaled up for the production of large area polymer light emitting devices (PLEDs). This deposition technique has already successfully been employed to produce organic photovoltaic devices (OPV)¹. Recently the electron blocking layer PEDOT:PSS² and metal top contact³ have been successfully spray coated as part of the organic photovoltaic device stack. In this study, the effects of ultrasonic spray deposition of polymer light emitting devices are investigated. For the first time – to our knowledge -, spray coating of the active layer in PLED is demonstrated. Different solvents are tested to achieve the best possible spray-able dispersion. The active layer morphology is characterized and optimized to produce uniform films with optimal thickness. Furthermore these ultrasonic spray coated films are incorporated in the polymer light emitting device stack to investigate the device characteristics and efficiency. Our results show that after careful optimization of the active layer, ultrasonic spray coating is prime candidate as deposition technique for mass production of PLEDs.

Light-emitting nanostructures made by conjugated polymers show interesting emission and electronic properties. In this work we report on novel approaches for the fabrication and control of light-emitting nanofibers by electrospinning. The shape, size and light-emitting properties of the fibers can be specifically tailored by acting on the composition of the solution used for the electrospinning process, an approach allowing for obtaining fibers ranging from micrometer-sized ribbons to almost cylindrical fibers with diameters down to few hundreds of nanometers. Moreover, following proper process optimization these fibers can also be precisely positioned in ordered arrays by near-field electrospinning, a method that exploits the stable region of the polymer jet. The possibility of precisely shaping the conjugated polymer fibers and of assembling the fiber in ordered arrays, combined with enhanced emission properties, opens interesting perspectives for developing novel emitting flexible nanomaterials suitable for light sourcing and optical sensing.

Optical properties of disperse red-13 (DR-13) covalently attached in the silica spheres have been investigated with the two step synthetic processes including a urethane bond formation between a 3-isocyanatopropyl triethoxysilane (ICPTES, -N=C=O) and DR-13 (-OH) with different ratios (3:14, 13:14 and 23:14) of the ICPTES and the DR-13 in pyridine and hydrolysis-condensation reactions between synthesized ICPTES/DR-13 (ICPDR) and tetraethoxyorthosilicate (TEOS) in NH₄OH. The absorption peak at 1704 cm^-1 representing the -C=O stretching vibration of the spheres attached ICPDR (ICPDRSS) indicates the formation of the urethane bond. Several other absorption peaks originated from ICPDR appeared in the FTIR spectra. The UV-visible absorption peak of the ICPDRSS shifted toward blue with respect to that of DR-13 in methanol, which indicated the antiparallel structure of the DR-13. The photoluminescence peak shifted toward red with the increase of the ratio of DR-13 with respect to ICPTES. This result implies the increase of the intermolecular interaction between DR-13 molecules with the increase of the DR-13 concentration.

In this talk, we will discuss recent advances in green and white electrophosphorescent stacked organic light-emitting diodes (OLEDs) with inverted top-emitting structures. These devices combine the advantages of having inverted electrode positions, a top-emissive design, and a stacked architecture. We will also demonstrate OLEDs that are fabricated on cellulose nanocrystal substrates and discuss how the use of such naturally-derived materials can reduce the environmental footprint of organic electronic devices such as OLEDs.

A new series of platinum complexes containing 4-hydroxy-1,5-naphtyridine derivative with different substitutens such as methyl, dimethyl, phenyl, phenoxy, dimethyl amine, piperidine, morpholine, phenoxazine or carbazole unit as the primary ligand and 2-(2,4-difluorophenyl)pyridine as the secondary ligand were synthesized and characterized. Single crystal X-ray diffraction studies of FPtOPhND, FPtCzND and FPtdmaND showed trans-coordinated in distorted square-planar geometry. Their photophysical properties and electrochemical properties were examined. All platinum complexes in these series exhibited dual emissions not only in solution but also in solid state thin film. Employing CBP or 4P-NPD as host material, high efficiency monochromatic and high quality hybrid white organic light emitting diodes (WOLEDs) were achieved with the single platinum complex dopant device, a relatively simple device configuration.

Organic light-emitting diodes (OLEDs) are a promising lighting technology. In particular OLEDs fabricated on plastic foils are believed to hold the future. These planar devices are subject to various optical losses, which requires sophisticated light management solutions. Flexible OLEDs on plastic substrates are as prone to losses related to wave guiding as devices on glass. However, we determined that OLEDs on plastic substrates are susceptible to another loss mode due to wave guiding in the thin film barrier. With modeling of white polymer OLEDs fabricated on PEN substrates, we demonstrate that this loss mode is particularly sensitive to polarized light emission. Furthermore, we investigated how thin film barrier approaches can be combined with high index light extraction layers. Our analysis shows that OLEDs with a thin film barrier consisting of an inorganic/organic/inorganic layer sequence, a low index inorganic negatively affects the OLED efficiency. We conclude that high index inorganics are more suitable for usage in high efficiency flexible OLEDs.

Efficient light extraction from organic light emitting diode (OLED) is challenging and efforts are being made to come up with efficient & cost effective outcoupling techniques. We demonstrate 50% EQE entitlement from solution processed white OLEDs compared to 33% EQE observed in devices, implying that there is plenty of room to improve the efficiency of white OLEDs. We present challenges in efficient light extraction from solution processed OLEDs that need to be overcome to close the efficiency gap. We also demonstrate a novel characterization technique that is effective in estimating the light extraction efficiency of outcoupling films and can expedite the selection and optimization of various light extraction approaches without the need to build OLEDs.

A new type of thiopyridinyl-based iridium molecule (POT) was used as the yellow phosphorescent material in our research. On fabricating a yellow PHOLED by doping POT-02 with host as the emitter, the device achieved a high power efficiency of 66.0 lm/W and an external quantum efficiency of 23.2%. On the other hand, a white organic lightemitting diode (WOLED) with a high power efficiency has been demonstrated by dispersing a host-free, yellow phosphorescent material in-between double blue phosphorescent emitters. In this study, we introduce a simple process for generating yellow emission of a WOLED by using the B/Y/B EML configuration. The B/Y/B EML configuration can achieve a higher efficiency and a smaller color shift with various operational brightness values. Based on the concept of this device, the molecular engineering of the blue phosphorescent host material as well as the light-extraction film, a WOLED with a power efficiency of 103 lm/W and an external quantum efficiency of 38.2% at a practical brightness of 1000 cd/m² with CIE coordinates (CIE_{x, y}) of (0.36, 0.48) can be achieved.

The feasibility of applying multiple white organic light-emitting diodes (WOLED) to establish specific planar illuminative patterns for general lighting without secondary optical components was experimentally investigated in smaller scale by using a single-axis automatic optical measuring system. Regular white light-emitting diodes (WLED) usually require secondary optical components to transform its point-source optical characteristics into specific planar illuminative pattern for general lighting application. WOLED has become a potential planar lighting source due to its unique device structure. The lighting source in our experiment consists of three WOLED's mounted side-by-side with changeable tilting angle. This adjustable lighting source with three planar WOLED's may be feasible for forming required illuminative pattern without using secondary optical components. Our preliminary experimental result measured from a 3-WOLED source with specific tilting angle in smaller scale suggests that a relatively uniform illuminative area can be established in practical mean without secondary optical components.

Two-color emission was observed in three-layer heterostructure organic light emitting transistors (OLETs). These devices consisted of a light-emitting layer made of tris(8-hydroxyquinolinato)aluminium (Alq₃) doped with 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM), sandwiched between hole and electron transport layers made of α,ω-dihexyl-quaterthiophene (DH-4T) and α,ω-diperfluorohexyl-quaterthiophene (DFH-4T), respectively. Ambipolar transfer curves were recorded from the fabricated devices, and two-color emission (red and green) was observed during transfer curve acquisition. Red emission was observed to take place at bias conditions supporting hole transport, while green emission occurred when electron-based current was dominant. Moreover, red emission originated from the Alq₃:DCM layer, which was verified by comparing the measured spectrum of OLETs to that of corresponding Alq₃:DCM organic light-emitting diodes (OLEDs). To investigate the origin of green emission, OLETs were fabricated without an electron transport layer. No green emission was observed, while red emission remained unchanged. Moreover, single-layer transistors and diodes fabricated from DFH-4T expressed green color emission similar to that of three-layer heterostructure OLETs. Therefore, we suggest that green emission originates from the electron transport layer.

Organic light-emitting diode (OLED), albeit is currently used in consumer electronics, still faces challenge with its limited performance stability. The degradation mechanisms that limit the lifetime of OLEDs can generally be separated into two categories: ambient and intrinsic. Much research has been devoted to understanding thus limiting these degradation mechanisms. However, surprisingly, there has been little work on how ambient and intrinsic degradation affect each other. In this work, the interplay between the ambient and intrinsic (more specifically exciton-induced) degradation is studied by comparing the effects of four degradation schemes, namely, no ambient or exciton-induced, ambient only, exciton-induced only and ambient and exciton-induced degradation on device lifetime. The results show that there is no interplay between ambient and exciton-induced degradation. Furthermore, it is evident that no photo-oxidation is present during ambient and exciton-induced degradation.

We report on the enhanced light outcoupling efficiency of monochrome top-emitting organic light-emitting diodes (OLEDs). These OLEDs incorporate a hole transport layer (HTL) material with a substantially lower refractive index (∼ 1.5) than the emitter material or the standard HTL material (∼ 1.8) of a reference device. This low-index HTL is situated between the opaque bottom metal contact (anode) and the active emission layer. Compared to an HTL with common refractive index, the dispersion relation of the surface plasmon polariton (SPP) mode from the opaque metal contact is shifted to smaller in-plane wavenumbers. This shift enhances the outcoupling efficiency as it reduces the total dissipated power of the emitter. Furthermore, the excitation of the coupled SPPs at the thin transparent metal top contact (cathode) is avoided by using an ultrathin top electrode. Hence, the coupling of the electroluminescence from the emitter molecules to all non-radiative evanescent modes, with respect to the emitter material, is reduced by at least a factor of two, additionally increasing the outcoupling efficiency. Furthermore, for sufficiently high refractive index contrast the shift of the SPP at the anode/organic interface can lead to in-plane wavenumbers smaller than the wavenumber within the organic emitter layer and outcoupling of all excited modes by high index light extraction structures, e.g. microlens, seems feasible. In accordance to optical simulations, the external quantum efficiency is enhanced by about 20 % for monochrome green emitting OLEDs with low refractive index HTL compared to a reference sample.

Pure 2-iodo-9,9′-spirobifluorene was synthesized by an efficient method without troublesome iodination of 9,9- spirobifluorene (SP) or the Sandmeyer reaction of 2-amino-9,9′-spirobifluorene. A series of main group element-bridged bis-9,9′-spirobifluorene derivatives were synthesized via coupling reactions of 2-iodo-9,9′-spirobifluorene and main group element-containing precursors. These heteroatom-bridged bis-spirobifluorenes show large triplet state energy gaps, high glass transition temperatures, and varied charge-transporting properties advantageous to the host materials for blue phosphorescence organic light-emitting diodes (PhOLEDs).

This paper reports a low-temperature thin-film encapsulation (TFE) process based on a low temperature atomic layer deposition ZrO₂ layer for top-emission organic light-emitting devices (TEOLEDs). The barrier characteristics of TFE showed a lower water vapor transmission rate (WVTR) of 2.3 × 10⁻³ g/m²/day and a longer continuous operation lifetime of 6-folds compared to the device without TFE under identical environmental and driving conditions. Furthermore, the emitting light extraction of the device with barrier layers was improved compared to the bare device. The theoretical calculation data were consistent with the experimental results and showed the potential for designing optimized TFE structures for improving light transmission.

We present the factors influencing the orientation of the phosphorescent dyes in phosphorescent OLEDs. And, we report that an OLED containing a phosphorescent emitter with horizontally oriented dipoles in an exciplex-forming co-host that exhibits an extremely high EQE of 32.3% and power efficiency of 142 lm/W, the highest values ever reported in literature. Furthermore, we experimentally and theoretically correlated the EQE of OLEDs to the PL quantum yield and the horizontal dipole ratio of phosphorescent dyes using three different dyes.

In recent years, OLED has advantages including that larger light area, thinner thickness, excellent light uniformity, and can be as a flexible light source. Many display panel and lighting have been started to use the OLED due to OLED without back light system, thus how to make and employ light extracting layer could be important issue to enhance OLED brightness. The purpose of this study is to enhance the light extraction efficiency and light emitting area of OLED, so the micro lens array and the prism reflection layer were provided to enhance the surface light extracting efficiency of OLD. Finally the prism layer and diffusing layer were used to increase the uniformity of emitting area of OLED, which the efficiency of 31% increasing to compare with the OLED without light extracting film.

Organic light-emitting diodes (OLEDs) are under widespread investigation to displace or complement inorganic optoelectronic devices for solid-state lighting and active displays. The materials comprising the active layers in OLED devices are selected or designed to provide the required intrinsic and extrinsic electronic properties needed for efficient charge injection and transport, and desired stability and emissive properties. The chemical design space for OLED materials is enormous and there is need for the development of computational approaches to help identify the most promising chemical solutions for experimental development. In this work we present a multi-scale simulation approach to efficiently screen libraries of potential OLED molecular materials. The workflow to assess potential OLED materials is: 1) evaluation based on first-principles prediction of key intrinsic properties (E_HOMO, E_LUMO, λ^e/h, E_triplet), 2) classical simulation of thin film morphology (RDF, ρ), and 3) first-principles evaluation of electron coupling for donor-acceptor pairs (H_ab) from the simulated condensed phase morphology.

We have studied the effects of incorporating phosphorescent sensitizers into fluorescent organic-light emitting diode (OLED) devices. In the emissive layer of this system, the host material is co-doped at low concentrations with both a phosphorescent and a fluorescent dye. The purpose of the phosphorescent dopant is to capture both singlet and triplet excitons from the host material and to transfer them into the singlet state of the fluorescent dye. Ideally, recombination of excitons and the emission of light would occur solely on the fluorescent dye. This sensitized fluorescent system can potentially achieve 100% internal quantum efficiency as both triplet and singlet states are being harvested. We have observed an almost two-fold improvement in the quantum efficiency of a sensitized fluorescent system, utilizing rubrene as the fluorescent dye and Ir(ppy)₂(acac) as the sensitizer, versus a standard rubrene-based host-guest system. By testing various dopant concentrations, the optimal emissive layer composition for this system was determine to be ~2 wt.% rubrene and ~7 wt.% Ir(ppy)₂(acac) in a CBP host.