Regensburg 2007 – wissenschaftliches Programm

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SYOE: Symposium Organic Thin Film Electronics: From Molecular Contacts to Devices

SYOE 8: Poster Session SYOE

SYOE 8.74: Poster

Dienstag, 27. März 2007, 18:00–20:00, Poster B

Charge transport and triplet quenching in conjugated polymers — •Dirk Hertel and Klaus Meerholz — Institute of Physical Chemistry, University of Cologne, Luxemburger Str. 116, 50939 Cologne

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. The investigation of charge transport in a poly-spirobifluorene with a hole transporting unit by current voltage characteristics as a function of temperature yields hole mobilities of 10-4 cm2 /Vs for the SCLC regime. Comparison of the SCLC mobility with mobilities obtained by time of flight (ToF) measurements shows that in the SCLC regime the mobility is trap limited. The ToF mobility is temperature and electric field dependent. From combined experimental investigations of time resolved phosphorescence spectroscopy and charge transport studies we are able to show that triplet quenching is a significant loss mechanism. The test system is PtOEP doped the poly-spirobifluorene copolymer. The triplet polaron quenching constant is about 10-13 cm3/s. The influence of PtOEP concentration and film thickness on the quenching efficiency is discussed.