Volume 79, Number 4, August 2007
|Number of page(s)||6|
|Section||Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties|
|Published online||25 July 2007|
Evidence of fractal structure for charge transport in carbon-nanotube/conjugated-polymer composites
Departamento de Física, Universidade Federal do Paraná - C.P. 19044, 81531-990, Curitiba-PR, Brazil
2 Departamento de Química, Universidade Federal do Paraná - 81531-990 Curitiba-PR, Brazil
Accepted: 2 July 2007
We measure the current-voltage (J-V) characteristics of organic composites as a function of carbon nanotubes concentration dispersed in a poly-3-hexilthiophene (P3HT) matrix. From a drift-diffusion-space-charge model and adapting the general effective medium and classical percolation theories, we quantify the system transport features. We find a drastic increase of the injection current due to drain channels provided by the nanotubes, probably a universal mechanism for charge injection in such type of system. We identify a percolation transition (with t = 0.3, the lowest critical exponent so far reported in the literature) and a fractal structure for transport after the percolation. This nearly 1D structure is surprising since the composites do not have any peculiar orientation along some preferential direction. Supported by transmission electron microscopy we explain the fractal behavior in terms of the morphology of the conductivity paths.
PACS: 72.60.+g – Mixed conductivity and conductivity transitions / 72.80.Le – Polymers; organic compounds (including organic semiconductors) / 73.61.Ph – Polymers; organic compounds
© Europhysics Letters Association, 2007
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