4 research outputs found
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In Situ Optical Measurement of Charge Transport Dynamics in Organic Photovoltaics
We
present a novel experimental approach which allows extraction of both
spatial and temporal information on charge dynamics in organic solar
cells. Using the wavelength dependence of the photonic structure in
these devices, we monitor the change in spatial overlap between the
photogenerated hole distribution and the optical probe profile as
a function of time. In a model system we find evidence for a buildup
of the photogenerated hole population close to the hole-extracting
electrode on a nanosecond time scale and show that this can limit
charge transport through space-charge effects under operating conditions
In Situ Optical Measurement of Charge Transport Dynamics in Organic Photovoltaics
We
present a novel experimental approach which allows extraction of both
spatial and temporal information on charge dynamics in organic solar
cells. Using the wavelength dependence of the photonic structure in
these devices, we monitor the change in spatial overlap between the
photogenerated hole distribution and the optical probe profile as
a function of time. In a model system we find evidence for a buildup
of the photogenerated hole population close to the hole-extracting
electrode on a nanosecond time scale and show that this can limit
charge transport through space-charge effects under operating conditions
Probing Through-Bond and Through-Space Interactions in Singlet Fission-Based Pentacene Dimers
Interchromophoric
interactions such as Coulombic coupling and exchange
interactions are crucial to the functional properties of numerous
π-conjugated systems. Here, we use magnetic circular dichroism
(MCD) spectroscopy to investigate interchromophoric interactions in
singlet fission relevant pentacene dimers. Using a simple analytical
model, we outline a general relationship between the geometry of pentacene
dimers and their calculated MCD response. We analyze experimental
MCD spectra of different covalently bridged pentacene dimers to reveal
how the molecular structure of the “bridge” affects
the magnitude of through-space Coulombic and through-bond exchange
interactions in the system. Our results show that through-bond interactions
are significant in dimers with conjugated molecules as bridging units
and these interactions promote the overall electronic coupling in
the system. Our generalized approach paves the way for the application
of MCD in investigating interchromophoric interactions across a range
of π-conjugated systems
Conformational Effect on Energy Transfer in Single Polythiophene Chains
Herein we describe the use of regioregular (<i>rr-</i>) and regiorandom (<i>rra-</i>) P3HT as models to study
energy transfer in ordered and disordered single conjugated polymer
chains. Single molecule fluorescence spectra and excitation/emission
polarization measurements were compared with a Förster resonance
energy transfer (FRET) model simulation. An increase in the mean single
chain polarization anisotropy from excitation to emission was observed
for both <i>rr-</i> and <i>rra-</i>P3HT. The peak
emission wavelengths of <i>rr-</i>P3HT were at substantially
lower energies than those of <i>rra-</i>P3HT. A simulation
based on FRET in single polymer chain conformations successfully reproduced
the experimental observations. These studies showed that ordered conformations
facilitated efficient energy transfer to a small number of low-energy
sites compared to disordered conformations. As a result, the histograms
of spectral peak wavelengths for ordered conformations were centered
at much lower energies than those obtained for disordered conformations.
Collectively, these experimental and simulated results provide the
basis for quantitatively describing energy transfer in an important
class of conjugated polymers commonly used in a variety of organic
electronics applications