Search

We present a thin-film dual-layer bottom barrier on polyimide that is compatible with 350°C backplane processing for organic light-emitting diode displays and that can facilitate foldable active-matrix organic light-emitting diode devices with a bending radius of

Side leakage experiments have been performed on the organic interlayer, so-called organic coating for planarization (OCP), in a hybrid thin-film encapsulation (TFE) stack based on two silicon nitride (SiN) barrier layers that was developed for organic light-emitting diodes (OLED). To measure the side leakage into OCP, a metallic Ca thin-film monitor can be used. However, the water uptake capacity of the Ca monitor affects the measurements. Here, we eliminated the contribution of the Ca layer from the measurement by variation of the Ca thickness and by measuring the side leakage until it reaches the Ca layer. For OCP with a water getter inside (5% CaO) the side leakage can be monitored by the loss of scattering of the CaO when it reacts with water to Ca(OH)2. This work describes measurements of the rate of side leakage into the OCP layer of the TFE stack, both for plain OCP and for OCP with CaO getter inside. The side leakage curves are used to derive diffusion coefficients. Performing measurements at various climates provides acceleration factors that are relevant for the performance quantification of the TFE stack. The limiting factors on the performance of an unstructured TFE stack as produced in a roll-to-roll (R2R) process are presented. For small OLED devices side leakage would drastically reduce the shelf lifetime but for larger devices the permeation properties of the TFE stack determine the shelf lifetime.

A technique is presented on tracing the sub-micron pinholes that result in black spots in organic light-emitting diodes (OLED) when exposed to ambient atmosphere. The mystery about the type and nature of tiny pinholes present in the OLED cathode that allow oxygen and/or moisture ingress in minute quantities causing black spot formation, is clarified. The technique can accurately locate nanodefects or pinholes in the center of black spots of various sizes, even on a centimeter scale. Pinholes in the investigated OLEDs were shown to be caused by different particles originating from various locations in the device stack. Defects in the Ba-Al cathode of a solution processed polymer LED (PLED) and pinholes in the LiF-Al cathode of a thermally evaporated small molecule organic LED (smOLED) were investigated and compared. The technique is a powerful tool for inspection and can, thereby, accelerate the process optimization for OLED fabrication.

The requirement for evaluating high performance barrier layers with water vapor transmission rates (WVTR) far below 10−3 g/m2 d has been sparked by the growing application of flexible and organic electronics. While several highly sensitive WVTR-measurement techniques are described in the literature, their accuracy and comparability has not yet been tested. There is an absence of direct comparison of these methods. With a growing body of literature referring to different coating and barrier technologies (often under different testing conditions), it is extremely difficult to gather a coherent picture both of the performance of the materials studied and the permeation measurement methods used. In order to clarify these points we report on independent WVTR measurements of the same batch of a high performance barrier film under two sets of conditions in several laboratories with different state-of the-art methods. These methods also include several calcium test set-ups. The results showed that, while some differences are present, there is a remarkable level of agreement between the measurement methods even prior to harmonization.

The availability of a high performance thin-film barrier is the most critical challenge in upscaling and commercializing flexible OLED products. We report a flexible thin-film-barrier technology that meets lifetime specifications for OLED lighting, and demonstrate it in rollable QVGA a-IGZO AMOLED displays. Roll-to-roll manufacturing of this high performance barrier film will be presented. cop. 2013 Society for Information Display.

To protect organic flexible devices from the ambient, they have to be encapsulated. Depending on the application in mind (OLED lighting, PV) different thin-film encapsulation methodology can be chosen. Each encapsulation process has different requirements and fabrication process freedom might be restricted, for example by mechanical reliability requirements or the total cost of the end product. Here we will show our recent investigations into different thin-film barriers with respect to their application and the route to production.

Gas diffusion barriers (GDB) are essential building blocks for the protection of sensitive materials or devices against ambient gases, like oxygen and moisture. In this work, we study the mechanics of GDBs processed by atomic layer deposition (ALD). We demonstrate that a wide range of ALD grown barrier layers carry intrinsic mechanical tensile stress in the range of 400-500 MPa. In the application of these GDBs on top of organic electronic devices, we derive a critical membrane force (σ · h)crit = 1200 GPaÅ (corresponding to a layer thickness of about 300 nm) for the onset of cracking and delamination. At the same time, we evidence that thicker GDBs would be more favorable for the efficient encapsulation of statistically occurring particle defects. Thus, to reduce the overall membrane force in this case to levels below (σ · h)crit, we introduce additional compressively strained layers, e.g., metals or SiNx. Thereby, highly robust GDBs are prepared on top of organic light emitting diodes, which do not crack/delaminate even under damp heat conditions 85 °C/85% rh.

A new method of making ultra-thin flexible organic light emitting diodes (OLEDs) using standard OLED fabrication facilities is reported. Through use of the Electronics on Plastic by Laser Release (EPLaR) technology, we have developed and demonstrated 18-μm thick single-pixel OLEDs. In this paper, besides describing the fabrication method, the electrical and optical performance of the flexible OLEDs is reported.

Promising results in terms of moisture and oxygen permeation barrier properties have been reported for organic/inorganic multilayers, but the impact of the organic interlayer on the overall barrier performance is still under discussion. It is generally accepted that the organic interlayer acts as a smoothening layer, allowing for the decoupling between defects/pinholes present in the polymer substrate and the inorganic layer. It is, however, also hypothesized that the organic interlayer infiltrates into the nano-pores present in the inorganic barrier layer, therefore affecting the barrier properties at microstructural level. In the present work, the moisture permeation barrier performance of SiO2/organosilicon multilayers deposited by means of initiated- and plasma enhanced-chemical vapor deposition is investigated. Calcium test measurements were used to discriminate between the overall water permeation (effective water vapor transmission rate, WVTR) through the layer and the permeation through the matrix porosity (intrinsic WVTR). The improvement in terms of intrinsic barrier performance was found to correlate with the residual nano-porosity content, due to the filling/infiltration of the organosilicon monomer in the SiO2 nano-pores. However, such improvement upon the deposition of the organosilicon interlayer is limited to a factor four. These results, in combination with the analysis of the local defects present in the multilayer structure, lead to the conclusion that the main contribution of the organosilicon interlayer to the overall barrier performance is the decoupling of the above-mentioned local defects/pinholes.

Organic light-emitting devices (OLEDs) have attracted considerable interest in the last five years and are now viewed as an important competitor with liquid crystals for a wide variety of display applications. Current research focuses on the use of small-molecule and polymer materials to make organic electroluminescent displays with both passive-and active-matrix technologies. This article will discuss work on the device architecture for a polymer passive-matrix display application, the stability of polymer light-emitting displays, and the use of ink-jet printing for high-resolution patterning of red, green, and blue light-emitting polymers.

Polymer LEDs have a number of attractive properties that make them suitable for many applications. Operating at low voltage, bright large-area devices can be made by simple technology. One of the limitations that prohibited industrialization of polymer LEDs was their limited lifetime. An overview of the improvement of polymer LED performance at Philips is presented. The progress during the last year is reflected by lifetimes of many thousands of hours for 8 cm2 devices that operate at daylight visibility under ambient conditions. Diagnostic measurements have been performed on polymer LEDs before and after stress testing, and on the materials used in these devices. These measurements have contributed to the understanding of the nature of the degradation of polymer LEDs.

Time-resolved emission spectra from the plasma, induced by laser ablation of uranium samples have been studied. The dependence of the emission intensity on time is strongly affected by the nature and pressure of the buffer gas. Air and argon have been used in the pressure range 0.002 to 5 mbar. The emission intensity as a function of time displays three maxima, indicating that three different processes within the expanding plasma plume are involved. On basis of the time-resolved spectra we propose a model that explains qualitatively the phenomena that are responsible for this time behaviour.

Highly transparent OLEDs are very attractive for lighting and light beautification applications. While the transparent anode is based on transparent ITO, the transparent cathode is based on a 3-layer approach: (semi)transparent electron injection layer that is a low work function metal, electrically transparent conductor used in order to limit the voltage drop across the OLED area, and overcoat to tune the optical properties without influencing the electrical properties. Transparent encapsulation based on thin film technology is used in order to protect devices from ambient exposure. Using this approach large area (50 cm2) transparent organic light-emitting device having 75% transparency in the off state is demonstrated. The efficiency of the transparent OLED is comparable with that of bottom emission OLED. It is demonstrated that by tuning the thickness and optical properties of both the cathode and the encapsulation the amount of light emitted through the anode and the cathode can be varied while the total amount of light emitted by the OLED remains the same. Moreover device optimization based on optical thin film calculations has been performed such that no angular dependence of emitted light is present both on anode and cathode side.

We present results and a discussion of highly efficient polymer Light-Emitting Diodes (polymer LEDs, PLEDs). The external quantum efficiency in current standard devices reaches up to 2-4% only. We have explored two routes to enhance this value. In the first route, PEDOT/PSS is replaced with a novel anode or hole injection layer. The efficiency with some Light Emitting Polymers (LEP) is improved significantly, resulting in an efficacy of 35 cd/A for a yellow emitting poly-(para-phenylene-vinylene) and 20 cd/A for a blue emitting poly-(spirobifluorene). We attribute the major improvement compared to standard devices, where about 10 and 5 cd/A are obtained, respectively, to a combination of improved exciton formation efficiency and light out-coupling efficiency, and to less quenching of the radiative decay under actual device operating conditions. In the second route, we developed a new host polymer with high triplet energy such that transition metal-based green-emitting phosphorescent dyes can be used without significant back transfer of triplet excitons to the polymer host. First results using this system showed about 25 cd/A using a soluble green Ir-based emitter. Importantly, all data are obtained in a standard two-layer device of a hole transport/injection layer and the LEP.

The status of the development of full-color polymer light emitting diodes will be presented. The focus of current materials research is on state-of-the-art red, green, and blue light-emitting polymers (LEP) with high efficiency, optimum color points, low driving voltages and long lifetimes in devices. A general overview of the progress of red, green and blue LEP lifetimes and efficiencies will be given and compared to requirements for both full-color passive and active matrix-displays for mobile display applications. Further, the status of ink-jet printing of LEPs for the industrialization of full-color displays will be discussed, and a comparison of the performance of spin coated and inkjet printed devices will be presented. In addition, two material-related topics studied recently will be discussed; namely, the lifetime of blue light-emitting devices correlated to processing, anodes, cathodes and the blue polymers themselves, and second, the consequences of pulsed-driving schemes on efficiency and lifetime.

In this paper on polymer LEDs we discuss the formation of black spots, surface treatments of the anode, and photochemical degradation of the emissive polymer. We find that small pinholes in the cathode layer are the origin of the black spots. The black spots form when H2O or O2 diffuse through the pinholes and react with the cathode at the polymer-cathode interface.A model is presented that describes the growth of the spots. We find that for both indium-tin-oxide (ITO) and Au anodes, an UV/O3 or an O2 plasma cleaning treatment increases the work function by 0.8-0.9 eV. A higher work function may lead to a better hole injection and a reduction in the operating voltage. We present a method to measure the quantum yield for bleaching, (gamma) equals 1.6$MN4 and (gamma) equals 1.7 10-7 for bleaching of dialkoxy-PPV in air and vacuum, respectively, indicating that the polymer is 1000 times more stable in vacuum than in air.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

With laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), trace and ultra-trace analysis of solids can be performed without any sample pre-treatment. For accurate quantitative analysis, however, matrix-matched standards are required. These standards are expensive, if available, especially when the concentrations are specified at the ng g–1 level. Therefore, if a large variety of samples has to be analysed, LA-ICP-MS is not the most suitable technique for a full quantitative analysis. In this work the use of LA-ICP-MS as a semiquantitative survey technique is described. Laser ablation ICP-MS is less precise than ICP-MS for solutions using nebulization for sample introduction. In LA-ICP-MS, however, the time for each analysis is much shorter, as no dissolution step is required. Moreover, with LA-ICP-MS completely unknown samples can be analysed. The latter aspect is shared with d.c. arc optical emission spectrometry (d.c. arc OES). A comparison of LA-ICP-MS with d.c. arc OES shows that the performance of LA-ICP-MS is superior in throughput and sensitivity.

In order to determine uranium and thorium at the sub-ng g–1 level in aluminium, the limit of detection (LOD) for continuous-flow nebulization inductively coupled plasma mass spectrometry (ICP-MS) is not sufficient, when a sample solution with the usual maximum concentration of 1 mg ml–1 is used. Therefore, two alternative sample introduction techniques have been used, flow injection (FI) and laser ablation (LA). With FI-ICP-MS the achievement of sub-ng g–1 detection limits is hampered by the presence of ‘spikes’. Although these spikes are also present with LA, it is possible to obtain a 0.2 ng g–1 LOD for uranium and thorium. This LOD is achieved artificially, by rejecting all measurements containing spikes.

During low-pressure chemical vapour deposition of SiO2 from thermally activated mixtures of silane and oxygen, laser-induced fluorescence is observed from OH and SiO molecules. From these measurements the rotational and vibrational temperatures are derived. The continuous nature of the observed oxygen chemiluminescence might be explained by a high vibrational temperature, which is not in equilibrium with the rotational temperature. Oxygen molecules are probably excited in the gas-phase reaction step SiO+O+O2→SiO2+O2*.

The 13C chemical shifts of the diazanaphthalenes have been recorded as a function of the pH value, providing classical titration curves. From these curves the pK1 and pK2 values have been determined taking into account the activity coefficients. The changes in 13C chemical shift under the influence of nitrogen protonation (Δδ) can be described by two protonation parameter sets.

During low-pressure chemical vapour deposition of SiO 2 from a thermally activated mixture of silane and oxygen, chemiluminescence is observed. It consists of a broad band extending from the UV throughout the visible part of the spectrum and a smaller signal at 310 nm. These signals are ascribed to molecular oxygen and OH radicals, respectively. Evidence is presented that these species are excited in a gas-phase process, possibly the collision-induced gas-phase reaction step Si+O 2 +O 2 /OH→SiO 2 +O* 2 /OH*.

The mechanism of the alkali bead detector, as used to detect organonitrogen compounds in the column effluent of a gas chromatograph, has been investigated by emission and laser-induced fluorescence measurements. The emission spectra led to the conclusion that the addition of an alkali salt to the glass of the bead of the detector is not essential: the beads can be made of ordinary soda glass. Laser-induced fluorescence measurements revealed that the alkali atoms are not lost from the bead by evaporation, but by an exchange with hydrogen. The application of this combination of spectroscopic techniques during a long run test of the bead proved that the ionization mechanism of the detector for both background and signal current is gas phase ionization of sodium atoms.

Experiments are described in which a low-pressure mercury discharge is irradiated with a dye-laser pulse tuned resonant to one of the 6 3P-7 3S1 mercury transitions. The effects of this optical pumping process are monitored via fluorescence on many mercury transitions. The sign and time behavior of each fluorescence signal are different, and are determined by one or more of the following processes: a) radiative decay of the 7 3S1 level; b) a change in electron-impact excitation rate from the ground state induced by the optogal-vanic effect (OGE). This OGE results from the population redistribution in the 6 3P levels after radiative decay of the 7 3S1 level; c) a change in electron-impact excitation rate from the 6 3P levels; and d) a change in 6 3P-6 3P collisional excitation rate. It is demonstrated that the signal and time behavior of the fluorescence signals induced by the pulsed optical pumping process can be used to determine the population mechanism(s) of excited states qualitatively.

The pH dependence of the 13C chemical shifts (δ) of the diazanaphthalenes has been recorded. From this dependence the pKa values have been determined using the Henderson-Hasselbach equation. The change in 13C chemical shifts under the influence of nitrogen protonation (Δδ) has been predicted using the Δδ values of quinoline and isoquinoline. The correlation between observed and expected Δδ values of the symmetric diazanaphthalenes is very good. Assuming these changes in chemical shifts to be of general validity, the site of protonation in the asymmetric diazanaphthalenes has been determined by comparison of the expected Δδ values for α- and s-nitrogen protonation with the observed ones. The site of protonation for 1,6- and 1,7-naphthyridine is the s-nitrogen atom, whereas for cinnoline both monoprotonated species are present in a significant amount.

The site of hydration for 1,6- and 1,7-naphthyridine has been determined by specific line broadening in the 1H n.m.r. spectra on the addition of water. The site of hydration appears to be the same as the site of protonation (s-nitrogen atom). The site of hydration in quinazoline has been shown to be the α-nitrogen atom. This strongly indicates that the site of protonation in this compound will also be at that nitrogen.

The 1H and 13C n.m.r. spectra of N-methylated pyridine, pyridazine, pyrimidine and pyrazine and N,N-dimethylated pyrimidine and pyrazine have been recorded and analysed. The change in the 13C chemical shifts under the influence of N-methylation (Δδ) in the diazabenzenes could be predicted by the Δδ values of pyridine. A comparison of the Δδ values of N-methylation with those of N-protonation showed that both reactions have a similar effect.

The 13C n.m.r. spectra of the N-methylated mono- and diazanaphthalenes have been recorded and analysed. It has been shown that N-methylation as well as N-protonation in cinnoline occur predominantly at the -nitrogen atom. N-methylation and N-protonation show a similar effect on the 13C chemical shifts

Royal Philips Electronics has recently launched the first commercially available polymer Light Emitting Diode (LED). In this paper, physical properties and phenomena will be discussed that must be taken into account during the selection of a polymer material and the choice of the device structure; for example, color, electron and hole mobility, polymer thickness, lifetime, leakage current and failure.