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Our research focuses on the preparation and study of
new organic/inorganic hybrid materials, composed of p-conjugated
polymers or oligomers and semiconductor nanocrystals. Conjugated
polymers offer unique physical properties which cannot be obtained for
conventional polymers. Both in their undoped (semiconducting) and doped
(conducting) states, conjugated polymers can be used as components of
so called “plastic electronics”. In their neutral (undoped) state they
are materials, which combine electronic properties of intrinsic
semiconductors with mechanical properties and solution processibility
of macromolecular systems. Moreover they frequently dissolve in the
same solvents as the ones that are used to disperse colloidal
nanocrystals. Thus conjugated polymers/nanocrystal composite films can
relatively easily be prepared by casting from a common solvent.
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Why such hybrid materials are of technological interest?
First, the electronic properties of the two
semiconductor constituents can be tuned individually and adapted to
each other. Second, the interface area between the polymer phase and
the nanocrystal one is very large due to the very high surface/volume
ratio of the nanocrystals. This enables efficient electronic transport
between these two components. Third, the conductivity of the polymeric
phase can be varied via oxidative or acid-base doping. Finally, the
polymeric phase of the composite ensures better mechanical properties
of the system as compared to pure inorganic semiconductor materials.
The image on the left shows the scheme of a photovoltaic device, which
is one of the most promising applications of organic/inorganic hybrid
materials.
Further reading
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Although conjugated polymer/nanocrystal composites
should exhibit significant advantages over both all-organic materials
and inorganic semiconductors, still considerable research efforts have
to precede their industrial applications. The main difficulty is caused
by the fact that several important properties of the composite, such as
charge carriers mobility, electroluminescence etc. are strongly
dependent on even small changes in the polymer supramolecular structure
and on the distribution of the nanocrystals within the polymer matrix,
which are not easy to control.
One of our strategies for a better morphology control consists of the
formation of covalent bonds or complexing between the two constituents of the hybrid
material. Parallel to this, we are exploiting pathways relying on
supramolecular self-assembly. Finally, we are using the unique auto-assembly properties of poly(alkylhiophenes). Depending on the processing
conditions, they can form for example fibrillar structures of high aspect ratio. Directional epitaxial solidification can lead to vertical phase segregation resulting in a lamellar structure consisting of alternating crystalline and amorphous zones. Nanocrystals can selectively be sequestered in the amorphous zones.
Collaborations:
R. De Bettignies, S. Guillerez and coll. (National Institute of Solar Energy (INES), Chambéry); M. Brinkmann (Institut Charles Sadron, Strasbourg)
Funding from the French Research Agency (ANR PNANO 2008 'MYOSOTIS'), from region Rhone-Alpes (research clusters Micro/Nano and Energy) and from CEA (program DSM Energy) is acknowledged.
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