2, Kiel University, Kiel, , Germany
3, University of New South Wales, Sydney, New South Wales, Australia
Various concepts have been investigated to produce deep-blue and efficient organic light emitting diodes (OLEDs) for displays, and to ultimately generate white light for general lighting applications. Among them, fluorescent emitters, phosphorescent emitters and thermally activated delayed fluorescence emitters.
In this work, we demonstrate the emission of deep-blue photons from an organic upconversion layer that is applied atop a high-brightness green phosphorescent OLED. Whereas, formerly, efficient photon-upconversion has been realized mostly in solution, here, its integration into OLEDs calls for solid-state upconversion concepts that can be applied to thin-films and that is compatible with thin-film device concepts which will facilitate fabrication, e.g., by additive manufacturing by roll-to-roll printing. We realized the solid-state upconversion layer by gelation of a suitable sensitizer/emitter pair. Additional band-pass filters between the OLED and the upconversion layer as well as on the outer side of the upconverter reduce the re-absorption of upconverted light in the OLED and enhance the photon confinement in the upconversion layer.