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 8.75: Poster

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

Hole transport in solution processed multi layer devices — •Angeles Pitarch, Dirk Hertel, and Klaus Meerholz — Institut für Physikalische Chemie, Universität zu Köln, Luxemburgerstr. 116, 50939 Köln

Luminescent conjugated polymers are increasingly used as active components in optoelectronic devices such as light emitting diodes (LEDs). The most promising approach to achieve multiple layers for purely solution processed devices is the crosslinking of small molecules after deposition, which leads to insoluble layers. We have studied charge transport in unipolar devices by current voltage measurements and transient current experiments. Our hole transport layers (HTL) consist of triphenylene-diamine derivatives with different oxidation potential. This allows tuning of the energy level offset between the anode (ITO/PEDOT) work function and the highest occupied molecular orbital (HOMO) of the hole transport materials. The current voltage characteristics show a transition from injection limited conduction to space charge limited conduction (SCLC) for decreasing energy level offset. The occurrence of SCLC depends as well on temperature. We have carried out investigations of doping, induced upon crosslinking and processing conditions on current voltage characteristics of crosslinked HTLs. The results are indicative of charge transport governed by bulk effects. The hole mobility reaches values of 10 -3 cm2/ Vs. Experimental data were fitted according to recent charge transport models taking into account trapping and a charge density dependent mobility, respectively.