The effects of Morphology of Light Emitting Polymers
Our NSOM studies have been devoted to investigating the electronic and
optical properties of thin film materials. The most promising applications
are in the area of light-emitting devices. In these systems it is critical
to understand the role of various charge and energy carriers in the system
as well as how the morphology of the films affects their generation and mobility.
Unfortunately, the methods of processing that make organic materials practical
have created materials that are difficult to characterize. Vapor-deposited and
spin cast thin films have widely varied morphologies that strongly affect their
material properties. Our group has been using the high spatial resolution of
near-field scanning optical microscopy to probe the morphology of thin films and
correlate these properties with their emission spectra. We have been particularly
interested in poly(fluorene) systems as well as poly(phenyleneethynylene).
(Students: David Ostrowski and Craig Cone)
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AFM Image of annealed film of poly(dihexylfluorene) showing the highly ordered nematic liquid crystalline structure of the film |
NSOM Photo-Conductivity Studies of Photovoltaics
We are using the high spatial resolution of near-field scanning optical microscopy
to locally probe the photoconductivity of model photovoltaics. Many organic photovoltaic
systems utilize phase separated organic thin films. The goals of this research is to
determine how the morphology of the films affects the current generated in the devices.
We are imaging functional devices directly through thin metal cathodes as well as model
planar systems. Ultimately we will combine the PC-NSOM with the time-resolved NSOM to
look at both excited state quenching for charge carrier formation and current to measure
the charge extraction.
(Student: David Ostrowski)
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NSOM fluorescence image of a phase separated film of two fluorene copolymers F8BT and PFB |
NSOM studies of J-Aggregates
In conjunction with Jürgen Rabe’s group from the Humboldt University in Berlin we are studying
tubular J-aggregates isolated on surfaces. The high resolution of NSOM allows for fluorescence
studies of individual aggregates. Currently we are probing the polarization of emission from
individual aggregates as well as their localized emission spectra as the basis for studying
energy transfer along the tubular structure. We are also interested in the oxidative chemistry
of the aggregates.
(Student: Dörthe M. Eisele, Physics, Humboldt University in Berlin, Germany)
