Dresden 2011 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 73: Joint Session: Organic Electronics and Photovoltaics II
HL 73.2: Talk
Thursday, March 17, 2011, 12:15–12:30, GER 38
OLEDs under high current densities – transient electroluminescence turn-on dynamics and singlet-triplet quenching — •Daniel Kasemann, Hartmut Fröb, and Karl Leo — Institut für Angewandte Photophysik, Technische Universität Dresden, 01062 Dresden, Germany
Organic solid state lasers have been intensively studied during the last decade due to the promising combination of versatile organic materials with the advantages of solid state emitters. Even though various optically pumped devices comprising different resonator types and material combinations have been shown, direct electrical pumping has not been achieved yet. The high excitation density needed in the active layer to achieve inversion is easily created by pulsed optical pumping, but additional losses prevent the excitation to reach the critical point when driven electrically.
To estimate the dimensions of these additional losses, we investigate full pin-OLEDs comprising the singlet emitter system DCM doped into Alq3 under high current densities. With the OLED active area reduced to 100x100 µ m2, these devices sustain current densities in the order of kA/cm2 in pulsed operation. The results of time resolved electroluminescence (EL) measurements as well as power dependent emission spectra give promising insight into the behaviour of OLEDs under these extreme excitation conditions. Intense EL transient turn-on peaks on the nanosecond time scale can be explained by modelling the singlet and triplet population taking into account singlet-triplet and triplet-triplet quenching in the emission layer.