C O M M U N I C A T I O N S
the nondirectionality required for optimal charge separation in a
film and for charge transport through a film can be obtained. This
approach can be optimized by variation of the aromatic diimides
or other n-type materials with more extended π-systems. This can
be done without compromising the nondirectionality that is essential
for amorphous blends, while yielding layers with an absorption
spectrum that overlaps better with the solar emission spectrum. As
such, this approach adds significant flexibility to the construction
of amorphous blends of n-type and p-type materials for optoelec-
tronic devices, such as all-organic solar cells. Further studies with
a variety of tetrahedral n-type materials in combination with a
variety of p-type polymers are currently ongoing in our laboratories.
Figure 3. Fluorescence quenching of MDMO-PPV by 1 in a thin film.
(
a) Fluorescence of pure MDMO-PPV film, and (b) 50/50 wt % mixture
of MDMO-PPV and 1, spin-coated from chlorobenzene.
Acknowledgment. The authors thank the Dutch Polymer
Institute (Functional Polymer Systems, Project 324) for financial
support, Dr. Marc Koetse (TNO Industries, Eindhoven) for sup-
plying the MDMO-PPV, Dr. Martijn Wienk (TU Eindhoven) for
many stimulating discussions, and Barend van Lagen for spectro-
scopic assistance.
Supporting Information Available: Synthesis and characterization
of 1 and 2 (6 pages, print/PDF). This material is available free of charge
via the Internet at http://pubs.acs.org.
Figure 4. BF-TEM images show the detailed morphology of thin films
containing mixtures of MDMO-PPV and 1, spin-coated from chloroform
(left) and chlorobenzene (right), respectively.
References
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Figure 5. Change in conductivity, ∆G, obtained from FP-TRMC
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and chlo-
3
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FP-TRMC probes the amount and mobility of charge carriers
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ns; λexc ) 500 nm) via the time-resolved absorption of microwaves
that are passed through the irradiated sample. As an example of
the versatility of our approach, we present in Figure 5 the change
in conductance observed for a mixture of 1 with P3HT.
As obvious from Figure 5, pulsed excitation leads to near-
instantaneous, highly efficient formation of long-lived charge
carriers, with lifetimes in the order of tens of microseconds. Using
(
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(
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3
0
MeV electron pulses, a maximum one-dimensional mobility of
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2
14
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material and displays effective charge transfer between adjacent
molecules of 1. In other words, by use of a tetrahedral framework,
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