Regensburg 2007 – scientific programme

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DS: Fachverband Dünne Schichten

DS 16: Organic Light Emitting Diodes (SYOE 9)

DS 16.2: Talk

Wednesday, March 28, 2007, 14:45–15:00, H32

Charge trapping and triplet quenching in conjugated polymers — •Dirk Hertel and Klaus Meerholz — Institute of Physical Chemistry, University of Cologne, Luxemburgerstr. 116

According to spin statistics the formation of excited states in OLEDs from uncorrelated charge carriers yields 25% singlet and 75% triplet states, the latter do usually not contribute to electroluminescence. Little is know about triplet charge carrier (polaron) interaction in conjugated polymers. The quenching of triplets by polarons might play an important role for the degradation of OLEDs or for applications such as organic lasers, since triplets are accumulated in the device due to their long lifetime. From combined experimental investigations of time resolved emission and charge transport we are able to show that in a poly-spirobifluorene doped with PtOEP triplet polaron quenching is a major loss mechanism. We derived a triplet polaron quenching constant of about 10-13 cm3/s from direct measurements of the phosphorescence lifetime under space charge limited conditions. The influence of PtOEP concentration and film thickness on the quenching efficiency is studied. The investigation of charge transport by current voltage characteristics as a function of temperature yields hole mobilities of 10-4 cm2 /Vs for the SCLC regime. Comparison with mobility measurements depending on temperature and electric field by time of flight technique shows that in the SCLC regime the mobility is trap limited.