Tweaking the performance of OLEDs with ultrastable glass layers (Conference Presentation)

Abstract

Organic light-emitting diodes (OLEDs) are an excellent technology for small and large display applications alike and further raise hope to complement solid state lighting in the future. All of these scenarios require OLEDs to operate at their best performance with respect to both wall-plug efficiency and device stability. Given the softness of the organic materials and their virtually unlimited molecular catalogue, this optimization progresses but slowly. In this presentation, we discuss the potential of organic materials processed as so-called ultrastable glasses to improve both efficiency and device lifetime. Ultrastable glasses are formed when the layers are grown by physical vapor deposition on substrates which are held slightly below the glass transition temperature of the respective material. In this study, we selected TPBi as a host material with comparably high Tg of 122 °C [2,2',2-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole)] for four different phosphorescent emitters, i.e. one blue, two green, and one red Ir-complexes). Compared to devices prepared at room temperature, we see significant enhancements of the external quantum efficiency and device lifetime and further, a clear correlation with the growth properties of the glass forming materials, i.e. the host:guest system.