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Trap concentration dependence of percolation in doped small molecule organic materials

Weise, Wieland and Keith, Torsten and Malm, Norwin von and Seggern, Heinz von (2005):
Trap concentration dependence of percolation in doped small molecule organic materials.
In: Journal of Applied Physics, 98 (4), pp. 043511-1-043511-5, ISSN 00218979,
[Online-Edition: http://dx.doi.org/10.1063/1.2005378],
[Article]

Abstract

The thermally stimulated current (TSC) technique is used to investigate the effect of doping of organic glassy thin films of the hole transport material N,N′-di(1-naphthyl)N,N′-diphenylbenzidine (α-NPD) with various concentrations of 4,4′,4″-tris(N-(1-naphthyl)-N-phenylamino)triphenylamine (1-NaphDATA). The mobility is estimated from current-voltage characteristics. At small dopant concentrations a TSC peak appears at about 200 K. Increasing the dopant concentration to about 4 vol % leads to a peak shift towards higher temperatures, related to decreasing mobility. When increasing the dopant concentration further, the peak shifts again to lower temperatures towards the peak position for pure 1-NaphDATA. The energy distribution of the trap structure is obtained utilizing the fractional TSC technique. In accordance to a higher-lying highest occupied molecular-orbital level of 1-NaphDATA as compared to the α-NPD matrix, the activation energy of a deep trap level of about 0.5 eV was reported previously for low doping concentrations up to a few percent. At higher dopant concentrations the deep traps vanish from the trap structure. The behavior can be interpreted as a change from a trap-controlled transport for small doping concentrations to a percolating transport on the dopant molecules themselves. It is shown that the onset of percolation at rather low concentrations can be explained by hopping including not only nearest neighbors.

Item Type: Article
Erschienen: 2005
Creators: Weise, Wieland and Keith, Torsten and Malm, Norwin von and Seggern, Heinz von
Title: Trap concentration dependence of percolation in doped small molecule organic materials
Language: English
Abstract:

The thermally stimulated current (TSC) technique is used to investigate the effect of doping of organic glassy thin films of the hole transport material N,N′-di(1-naphthyl)N,N′-diphenylbenzidine (α-NPD) with various concentrations of 4,4′,4″-tris(N-(1-naphthyl)-N-phenylamino)triphenylamine (1-NaphDATA). The mobility is estimated from current-voltage characteristics. At small dopant concentrations a TSC peak appears at about 200 K. Increasing the dopant concentration to about 4 vol % leads to a peak shift towards higher temperatures, related to decreasing mobility. When increasing the dopant concentration further, the peak shifts again to lower temperatures towards the peak position for pure 1-NaphDATA. The energy distribution of the trap structure is obtained utilizing the fractional TSC technique. In accordance to a higher-lying highest occupied molecular-orbital level of 1-NaphDATA as compared to the α-NPD matrix, the activation energy of a deep trap level of about 0.5 eV was reported previously for low doping concentrations up to a few percent. At higher dopant concentrations the deep traps vanish from the trap structure. The behavior can be interpreted as a change from a trap-controlled transport for small doping concentrations to a percolating transport on the dopant molecules themselves. It is shown that the onset of percolation at rather low concentrations can be explained by hopping including not only nearest neighbors.

Journal or Publication Title: Journal of Applied Physics
Volume: 98
Number: 4
Uncontrolled Keywords: organic semiconductors, semiconductor thin films, percolation, thermally stimulated currents, hole traps, hole mobility, semiconductor doping, doping profiles, deep levels, hopping conduction
Divisions: 11 Department of Materials and Earth Sciences
DFG-Collaborative Research Centres (incl. Transregio)
DFG-Collaborative Research Centres (incl. Transregio) > Collaborative Research Centres
Zentrale Einrichtungen
DFG-Collaborative Research Centres (incl. Transregio) > Collaborative Research Centres > CRC 595: Electrical fatigue
DFG-Collaborative Research Centres (incl. Transregio) > Collaborative Research Centres > CRC 595: Electrical fatigue > D - Component properties
DFG-Collaborative Research Centres (incl. Transregio) > Collaborative Research Centres > CRC 595: Electrical fatigue > D - Component properties > Subproject D4: Fatigue of organic electronic devices
Date Deposited: 16 Sep 2011 13:57
Official URL: http://dx.doi.org/10.1063/1.2005378
Additional Information:

SFB 595 D4

Identification Number: doi:10.1063/1.2005378
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