AbstractManufacturing of Organic Light Emitting Diodes (OLED) for lighting is still some distance from the industry recognized cost target of 100 € /m2. Within the government funded Light In‐Line (LILi) project, a team of material supplier, machine manufacturers and basic researchers have investigated potential ways to reduce OLED manufacturing costs. The concept developed within the LILi‐project shows that a competitive cost structure can now be reached.

Poly(p-phenylene vinylene)s (PPVs) are very promising materials for optoelectronic applications, especially for displays based on polymer light emitting diodes (PLEDs). We report here our findings concerning defect structures in this materials and the influence of the discovered irregularities on an important property of the materials, i.e. the operational life in a PLED. Recent improvements, which were deviated from this findings are presented: optimized PPVs with a lower amount of defects result in a strong increase of operational lifetime.

AbstractThe purity of OLED materials is examined by various analytical tools down to ppm level. Especially halogenated impurities are found to have a significant effect on device performance. HPLC MS coupling methods are needed to identify those harmful impurities. Three case studies are described, but the results are likely to be representative for most classes of OLED materials.

The first high-resolution full-color OLED display based on a direct photolithographic process is presented by Meerholz and co-workers on p. 191. The cover shows a schematic illustration of the fabrication process, a fluorescence microscope picture demonstrating the micrometer resolution capability of the process, and a picture of the first prototype displaying a test image. Electroluminescent polymers with photoresist-like properties are the basis of the new process (chemical structure shown in the background). The first full-color polymer organic light-emitting diode (OLED) display is reported, fabricated by a direct photolithography process, that is, a process that allows direct structuring of the electroluminescent layer of the OLED by exposure to UV light. The required photosensitivity is introduced by attaching oxetane side groups to the backbone of red-, green-, and blue-light-emitting polymers. This allows for the use of photolithography to selectively crosslink thin films of these polymers. Hence the solution-based process requires neither an additional etching step, as is the case for conventional photoresist lithography, nor does it rely on the use of prestructured substrates, which are required if ink-jet printing is used to pixilate the emissive layer. The process allows for low-cost display fabrication without sacrificing resolution: Structures with features in the range of 2 μm are obtained by patterning the emitting polymers via UV illumination through an ultrafine shadow mask. Compared to state-of-the-art fluorescent OLEDs, the display prototype (pixel size 200 μm × 600 μm) presented here shows very good efficiency as well as good color saturation for all three colors. The application in solid-state lighting is also possible: Pure white light [Commision Internationale de l'Eclairage (CIE) values of 0.33, 0.33 and color rendering index (CRI) of 76] is obtained at an efficiency of 5 cd A–1 by mixing the three colors in the appropriate ratio. For further enhancement of the device efficiency, an additional hole-transport layer (HTL), which is also photo-crosslinkable and therefore suitable to fabricate multilayer devices from solution, is embedded between the anode and the electroluminescent layer.

The authors report on highly efficient phosphorescent organic light-emitting diodes (OLEDs) based on a low-molecular weight electron-conducting, bis-spirobifluorene host doped with a soluble derivative of the green emitter fac-tris(2-phenylpyridine) iridium (III) [Ir(ppy)3]. All organic layers were spin coated and a strong improvement of performance was achieved by introduction of a hole-transporting double layer based on cross-linkable low-molecular weight molecules. The devices combine the easy fabrication procedure known from polymer-based OLEDs with the higher efficiency of small molecules. Maximum luminous and power efficiencies of 59cd∕A and 58lm∕W, respectively, are obtained, combined with a low driving voltage and high efficiencies even at high brightnesses. At 1000cd∕m2 the efficiencies are as high as 55cd∕A and 49lm∕W.