Quenching phosphorescence devices

PVK are critical in achieving high efficiency. While conjugated polymers, such as poly(fluorenes) and poly(phenylene-vinylenes), have been used extensively for fluorescence-based devices, they are not as useful for phosphorescence-based devices because they characteristically have low triplet energies. The triplet levels of most conjugated polymers are in the red to near-IR spectral region, and thus efficiently quench phosphorescence from dopants designed to emit in the visible part of the spectrum." ... 

The first iridium complex used in PHOLED devices was fac tris(2-phenylpyridine) iridium Ir(ppy)3 complex [282]. It has a short triplet lifetime ( 1 ps) and high phosphorescent efficiency (p = 40% at room temperature in solution) [283]. However, in the solid state, most iridium complexes showed very low phosphorescent QE due to aggregate quenching. In most cases, the complexes have to be diluted in host materials to avoid reducing the... 

Once again, the most recent developments have been in the area of green phosphorescent materials where phenomenal efficiencies are now beginning to be coupled with good device lifetimes. The prototypical emitter of this type is iridium-tris-2-phenylpyridine (Ir(ppy)3) used as a dopant (Scheme 3.98), usually diluted into a carbazole type host, because it is prone to serious self-quenching problems. 

F. Kwong. H. L. Zheng. H. Che. C. M. (2001). Reduction of Self-Quenching Effect in Organic Electrophosphorescence Emitting Devices via the Use of Sterically Hindered Spacers in Phosphorescence Molecules. Advanced Materials, vol. 13, no. 16,1245-1248. 

The demonstration of the usefulness of photoluminescence measurements to probe mechanisms of Alq-based OLED degradation paved the way for their routine use in the studies of various OLED devices, including those based on phosphorescent emitters. For example, quenching was demonstrated to play a significant role in the degradation of phosphorescent OLEDs with CBP as the emissive layer host [55,64]. 

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