Berlin 2012 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 24: Poster: Organic Semiconductors

CPP 24.15: Poster

Wednesday, March 28, 2012, 11:00–13:00, Poster A

Excitonic lifetime changes in organic light-emitting diodes induced by triplet-polaron-quenching — •Sebastian Wehrmeister, Tobias Daniel Schmidt, and Wolfgang Brütting — Institute of Physics, University of Augsburg, 86135 Augsburg, Germany

Although organic light emitting diodes (OLEDs) have matured in technical applications in recent years they still have not reached high efficiencies. The external quantum efficiency (EQE) and thereby the luminous efficacy is limited by multiple effects, such as low outcoupling efficiency, energy dissipation to surface plasmons and waveguided modes, unbalanced charge carrier ratio and quenching induced non-radiative energy losses especially at high brightness. However, to distinguish between triplet-triplet-annihilation and triplet-polaron-quenching, the two major quenching processes at high brightness, time-resolved measurements under combined electrical and optical excitation have been performed [1]. In our experiments we examine the effect of triplet-polaron quenching on excitonic lifetimes in a phosphorescent OLED with fac-tris(2-phenylpyridine)iridium(III) (Ir(ppy)₃) as emitter. We probe exciton lifetime in the steady-state region of a rectangular electric pulse by a short laser pulse on top. In order to achieve reliable data we have continuously increased the current density of the electrical pulse resulting in an exponential decrease of the excitonic lifetime and thus a decrease in the EQE.
 [1]N.C. Giebink, S.R. Forrest, Phys. Rev. B,235215-1 (2008)