Dresden 2006 – scientific programme

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CPP: Chemische Physik und Polymerphysik

CPP 6: Electronic Structure and Spectroscopy I

CPP 6.9: Talk

Monday, March 27, 2006, 16:45–17:00, ZEU 114

Delayed luminescence in conjugated polymers — •Dirk Hertel and Klaus Meerholz — Institute of Physical Chemistry, University of Cologne, Luxemburger Str. 116, 50939 Cologne, Germany

Luminescent conjugated polymers are increasingly used as active components in optoelectronic devices such as light emitting diodes (LEDs). One obstacle for high volume OLED applications is the limited luminescence efficiency of conjugated polymers. According to spin statistics the formation of excited states from uncorrelated charge carriers yields 25% singlet and 75% triplet states, the latter do usually not contribute to electroluminescence. There is abundant indirect evidence for the existence of triplet states in conjugated polymers, but little is known about their generation and kinetics. The application of time gated luminescence spectroscopy enabled us to observe delayed fluorescence (DF) and phosphorescence (Ph) in conjugated polymers of the spiro-polyfluorene type. These materials are used for state of the art polymer LEDs. From combined experimental investigations of the time and intensity dependence of DF and Ph as well as the temperature dependence of DF we are able to show that DF in a spiro-polyfluorene homopolymer is dominated by triplet-triplet annihilation (TTA). Recently we have extended our investigation to spiro- copolymers to study the influence of electron transport and hole transport units on the DF and Ph. To clarify the role of charge recombination on DF the dependence of DF and Ph on applied electric fields is discussed. Time gated luminescence spectroscopy is as well a powerful tool to check the purity of conjugated materials.