Thomas Rosenow

Highly efficient white organic light-emitting diodes based on fluorescent blue emitters

Beside inorganic LEDs and fluorescent lamps, organic light-emitting diodes (OLEDs) are evolving into a serious alternative to incandescent lamps. Up to now, it was assumed that all-phosphorescent OLEDs are required for reaching sufficiently high efficiencies. However, the stability of phosphorescent blue emitters is a major challenge. We present a novel approach to achieve highly efficient (up to 90 lm/W at 1000 cd/m2 using a macroextractor) white light emission from OLEDs. The here presented combination of a fluorescent blue and a phosphorescent red emitter simultaneously allows for a strong blue emission and efficient triplet transfer to the phosphor. The spectrum is extended in the green and yellow region by a full phosphorescent unit stacked on top of the triplet harvesting device. This superposition of four different emitters results in color coordinates close to illuminant A and a color rendering index of 80. Furthermore, color stability is given with respect to varying driving conditions and estima...

Improved high-brightness efficiency of phosphorescent organic LEDs comprising emitter molecules with small permanent dipole moments.

Organic light-emitting diodes (OLEDs) are emerging fl at, highly effi cient, and potentially fl exible area light-sources that are seen as one of the next generation technologies for display, signage, and lighting applications. Using phosphorescent emitter molecules, electron-photon conversion effi ciencies of unity are possible in OLEDs, as all excited states can be harvested radiatively on their triplet states. [ 1–3 ] However, owing to the excited state lifetime of these phosphors in the range of microseconds, bimolecular quenching processes, [ 4 , 5 ] dominated by triplettriplet annihilation (TTA), noticeably reduce the high brightness effi ciency – an effect referred to as effi ciency roll-off. Recently, we have reported on white OLEDs that are, with respect to their luminous effi cacy, on par with fl uorescent tubes reaching 90 lm W − 1 at a brightness of 1000 cd m − 2 . [ 6 ] The device concept also incorporated a novel design to reduce the roll-off. Nevertheless, for such devices, the external quantum effi ciency (EQE) at low brightness (100 cd m − 2 ) is reduced by (20 ± 2)% at 5000 cd m − 2 – a luminance level that is considered realistic for high-brightness illumination purposes. Hence, without effi ciency roll-off, such devices could still be signifi cantly improved. In terms of effi ciency it is therefore one of the most important issues to push the roll-off to higher brightness. Many OLED designs that result in an improved highbrightness performance of phosphorescent OLEDs have been reported. Among them are double-emission layer systems to widen the recombination zone, [ 7 ] strong microcavities to reduce the phosphorescent lifetime of the emitter, [ 8 , 9 ] sub-structured emission layers (EMLs) to reduce diffusive exciton migration [ 10 ]

Near-infrared organic light emitting diodes based on heavy metal phthalocyanines

We demonstrate near-infrared (NIR) organic light-emitting diodes containing the phthalocyanines of copper (CuPc), palladium (PdPc), and platinum (PtPc) as emitting material. The devices show NIR emission from the triplet excitonic states of those phthalocyanines at 1095, 1025, and 966nm, respectively. A yellow singlet emitter serves as host for the emitter materials, reducing triplet exciton quenching and improving energy transfer to the emitter. Using the emitter PtPc as guest and the yellow singlet emitter as host, an external quantum efficiency of 0.3% is achieved for infrared light emission at 966nm. Due to the use of electrically doped charge transport layers, operation at voltages significantly below 3V is possible. Light output reaches 80μW∕cm2 at a current density of 140mA∕cm2.

Analysis of the external and internal quantum efficiency of multi-emitter, white organic light emitting diodes

We report on a theoretical framework for the efficiency analysis of complex, multi-emitter organic light emitting diodes (OLEDs). The calculation approach makes use of electromagnetic modeling to quantify the overall OLED photon outcoupling efficiency and a phenomenological description for electrical and excitonic processes. From the comparison of optical modeling results and measurements of the total external quantum efficiency, we obtain reliable estimates of internal quantum yield. As application of the model, we analyze high-efficiency stacked white OLEDs and comment on the various efficiency loss channels present in the devices.

Novel concepts for OLED lighting

Starting from a lab-curiosity, organic light emitting diodes have matured into a promising technology that has entered commercial markets. In particular for lighting applications, OLEDs can take advantage of their outstanding properties such as a high luminous efficacy, good color quality, and new design possibilities such as illumination by at light sources. In this contribution, new results on two approaches for highly efficient white OLEDs are presented: the all-phosphorescent concept and the triplet-harvesting approach.

72.4: Invited Paper: Novel Approaches for OLED Lighting

In this paper, we discuss novel approaches for organic light-emitting diode (OLED) lighting application. In particular, we discuss OLED deposited by vacuum deposition on flexible substrates such as plastic and metal foils. We discuss the specific challenges of OLED design for such substrates, in particular when top-emitting structures are required. Furthermore, we discuss a novel vacuum roll-to-roll tool which is capable of depositing oligomer OLED with high efficiency.

25.2: Invited Paper: Concepts for Highly Efficient White OLEDs

In this paper, we discuss in detail a novel concept for white organic light-emitting diodes (OLEDs) comprising three different phosphorescent emitters. Its key feature, a matrix-emitter combination for the blue sub-emission layer combined with a specific arrangement of the green- and red-emitting layers, leads to very high luminous efficacies. We present the key parameters of this emission layer design that are essential for high efficiencies. Finally, we briefly discuss a second, highly efficient approach for white OLEDs: the triplet harvesting concept. It makes use of a fluorescent blue emitter having benefits for higher device stability and at the same time the potential for 100% internal quantum efficiency.