Entwicklung und Evaluierung langzeitstabiler orange-roter organischer Leuchtdioden (English shop)

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Organic light-emitting diodes (OLEDs) represent an outstanding and rapidly growing technology segment whose products have either already been introduced to the market or are close to reaching market maturity. At present, it is still difficult in many cases for OLED products to compete directly with the established technologies in the field of display and lighting elements. Unique selling points of OLED technology are expected to make it possible in the future to open up new fields of application. Alongside the very recent history of commercially available products, intensive fundamental research on OLEDs already dates back more than twenty years.

Despite these long-standing research activities, there are still important questions for which no satisfactory answers have yet been found. This applies in particular to the understanding of intrinsic degradation within the organic layers, which in many cases leads to a rapidly progressing loss of luminance. Previous investigations have shown that intrinsic degradation is strongly material-specific. A systematic understanding of the causes of degradation is the prerequisite for the targeted design of new long-term stable materials.

The present work therefore focuses on the specific consideration of luminance degradation in the investigation and characterisation of new materials. New orange-red emitting triplet emitters from the class of quinoxaline iridium complexes are introduced, characterised and investigated in devices. Targeted degradation studies on the triplet emitters employed are discussed, which are intended to make it possible to assess the striking differences in the long-term stabilities of the corresponding OLEDs. Furthermore, systematic optimisation concepts for the OLED architecture are presented and discussed in order to evaluate the actual lifetime potential. Using the new triplet emitter IHF-TE-15, devices are presented that achieve application-relevant luminance lifetimes and are among the most long-term stable phosphorescent OLEDs described in the literature.

The realisation of an intrinsically very stable OLED architecture opens up the possibility of specifically investigating the intrinsic stability of individual materials. Different matrix concepts, charge transport materials and, in particular, triplet emitters are compared with one another. In addition, the influence of a new method of ALD thin-film encapsulation on the luminance lifetime is described. The investigation of luminance lifetime is introduced as a further method for examining the encapsulation quality of different encapsulation processes. Besides the consideration of encapsulation quality, the general influence of the encapsulation process on the OLED is also described.