Regensburg 2007 – wissenschaftliches Programm

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SYOE: Symposium Organic Thin Film Electronics: From Molecular Contacts to Devices

SYOE 6: Transport in Organics Materials

SYOE 6.5: Vortrag

Dienstag, 27. März 2007, 16:00–16:15, H32

Trap-Controlled Hole Transport in a Small Molecule Organic Semiconductor — •Arne Fleissner, Hanna Schmid, Roland Schmechel, Christian Melzer, and Heinz von Seggern — TU Darmstadt, Institute of Materials Science, Electronic Materials Department, Petersenstr. 23, 64287 Darmstadt, Germany

The transport of charge carriers through organic semiconductors is strongly affected by trap states in the energy gap. In this work, a well defined concentration of hole traps is deliberately introduced into a small molecule hole transporter in order to control the mode of charge carrier transport and mobility. For that purpose, the host material N,N'-di(1-naphtyl)-N,N'-diphenylbenzidine (α-NPD) is molecularly doped by thermal co-evaporation with 4,4',4''-tris-[N-(1-naphtyl)-N-(phenylamino)]-triphenylamine (1-NaphDATA), which is known to create 0.4eV-deep neutral hole traps. Using a mechanical chopper to control the mass flow of the dopant, doping concentrations as low as 100ppm were achieved. The influence of the trap concentration on charge transport and mobility is studied on diode-like structures by an optical time-of-flight method. Non-dispersive hole transport is observed for undoped α-NPD. The introduction of 100ppm hole traps results in non-dispersive but trap-controlled transport and reduces the mobility by orders of magnitude. For increasing the trap concentration to over 1000ppm, the transition to dispersive transport is observed.