Berlin 2008 – wissenschaftliches Programm

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SYSA: Symposium Tayloring Organic Interfaces: Molecular Structures and Applications

SYSA 4: Organic Devices II

SYSA 4.4: Vortrag

Dienstag, 26. Februar 2008, 17:30–17:45, H 2013

Charge carriers dynamic and radiative recombination processes in organic light emitting devices studied by a sub-microsecond pulsed electroluminescence technique — •Eugenio Lunedei, Paolo Annibale, Yiqiang Zhan, and Carlo Taliani — ISMN-CNR, Bologna, Italy

Despite the realization of OLEDs with high performances and organic transistors with high mobility, the dynamic of charge carriers within a working device its is not always fully understood. The transport of charge through organic semiconductors is strongly affected by trap states in the energy gap, presence of interfaces, structural disorder and injection barriers at contacts. The transport properties are sometimes not obvious from I/V curves alone: the correlation between radiative emission and a pulsed charge injection allows to characterize both transport and optical properties of device. By making use of our time-resolved electroluminescence correlator capable of sub-µs voltage pulsewidth and time-resolution down to ns scale, we were able to follow the recombination processes in multilayer devices based on small molecules (as Alq₃ and T₆), blend of polymers, in inverted OLEDs with TCOs anode and in light emitting OFETs of T₆ and Pentacene. The charge carriers mobility is directly obtained by ToF measurements as well as its dependance on the applied voltage and on the trap-site density within the organic layers; furthermore, the possibility to record complete electroluminescence spectra during the application of the electric pulse and in successive time windows gives a new insight on the fate of injected charges and on the nature of trapping sites.