Tiefblaue phosphoreszente organische Leuchtdioden basierend auf Iridium-Carben-Komplexen (English shop)

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OLEDs (Organic Light Emitting Diodes) have undergone rapid development in recent years and are now commercially available as lighting and display elements. In addition to their extremely flat design and the high transparency that can be achieved, they are distinguished from other established technologies, such as liquid crystal displays (LCD), above all by their low energy consumption. The latter could be reduced still further through the development of phosphorescent emitter dyes.

While long-term stable, phosphorescent OLEDs with suitable colour saturation have already been realised for the red and green spectral ranges, the lifetime of efficient, deep-blue emitting devices is still too low. However, the inclusion of the third complementary colour is indispensable both for display applications and for generating white light perceived as pleasant.

This work focuses on the investigation of deep-blue OLEDs with regard to high efficiency, colour purity and, in particular, lifetime. To this end, the emitter dyes, based on the material class of iridium carbene complexes, as well as suitable host materials, were developed and produced by the project partner.

In order first to characterise commercially available compounds and newly developed substances with respect to their charge transport properties, methods for determining the charge carrier mobility are introduced. With regard to hole mobility, the use of transition metal oxides enables the formation of an ohmic injection contact required for all methods, even for materials with a deep ionisation potential. For determining the electron mobility, the injection contact Cs2CO3-Ca-Al has proven to be favourable.

Potential emitter and host materials are subsequently examined as to which type of stress causes them to exhibit degradation tendencies. Based on the charge transport results and by means of further experiments on realised OLEDs, a better device understanding is gained regarding the charge carrier conditions as well as the distribution of the recombination and emission zones, whereupon the device architecture can be specifically adapted with a view to a long lifetime. In this way, an external quantum efficiency of 9.5 % and a lifetime of 75 hours are achieved, each measured at a luminance of 300 cd/m2. The latter corresponds to an increase by a factor of 13,500 compared with the initial structure.