Page 386 - Organic Electronics in Sensors and Biotechnology

Electrophoretically Deposited Polymers for Organic Electronics 363

context, conductive polymers are likely to play an important role in the
emerging science of molecular computers. In general, organic conduc-
tive polymers have a higher resistance and therefore have poor electri-
cal conductivity compared to inorganic conductors.
The self-assembling or ordering of these organic and hybrid mate-
rials enhances the p-orbital overlap and is a key to improvements in
carrier mobility. The recombination of charge carriers under an applied
field can lead to the formation of an exciton that decays radiatively to
produce light emission. For preparation of polymer thin films from
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solution, a number of techniques such as spin coating, sol-gels, inkjet
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printing, Langmuir Blodgett (LB) film deposition, self-assembled
1
technique, EPD, etc. have been utilized. The spin-coating technique,
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though cheap, requires excess of material solution as most of the solu-
tion gets blown away during film preparation. Also when thick films
are required, this technique does not provide films of good uniformity
and quality. The inkjet technique, though, gives a uniform pattern, but
the production cost is quite high and it is a time-consuming process.
The LB technique for film preparation requires the presence of amphi-
philic groups in a material of interest, or the material of interest should
be mixed with some amphiphilic materials for good-quality films. The
use of an additional amphiphilic material hinders the materials of
interest, decreases their surface exposure, and enhances the resistance
of the film. And the stability of LB films is still a major problem. The
use of the self-assembly technique for polymer layer formation is much
restricted to the conditions required for self-assembled monolayer for-
mation as it requires specific chemistry between the surface of the sub-
strate and the functional group present in the polymer.
The EPD technique has recently gained much attention due to added
advantages of high rate of deposition, controlled thickness, simple and
easy method of fabrication, dense and uniform film preparation, etc. 9
Moreover, EPD from a colloidal suspension of desired conducting poly-
mers provides the unique strategy to tailor nanostructured films 10–12 by a
very simple method with unique morphology. Besides this, the use of
EPD involves deposition from colloidal solution without any additives
and thus ensures purity of the deposited polymer film, which is critical
for the fabrication of optoelectronic and biosensor devices.

10.2 Electrophoretic Deposition

10.2.1 Definition
Electrophoretic deposition is a colloidal process in which charged
powder particles, dispersed or suspended in a liquid medium, are
attracted and deposited onto a conductive support of opposite charge
on application of DC electric field. Despite being a wet process, EPD
provides easy control over the film thickness and morphology by
simple adjustment of deposition time and applied voltage. The term