dc.contributor.advisor |
Narayan, K.S. |
|
dc.contributor.author |
Kabra, Dinesh |
|
dc.date.accessioned |
2020-07-21T14:45:14Z |
|
dc.date.available |
2020-07-21T14:45:14Z |
|
dc.date.issued |
2007 |
|
dc.identifier.citation |
Kabra, Dinesh. 2007, Studies of length scales in semiconducting polymers using scanning photocurrent contrast microscopy, Ph.D. thesis, Jawaharlal Nehru Centre for Advanced Scientific Research, Bengaluru |
en_US |
dc.identifier.uri |
https://libjncir.jncasr.ac.in/xmlui/handle/10572/2903 |
|
dc.description |
Open access |
en_US |
dc.description.abstract |
Semiconducting polymer films. when photoexcited with defined beam profiles
generate excess charge carriers from the electronically excited state, which eventually
spread over a volume exceeding the beam-sample cross-section. The thesis focuses on the
studies of these length scales in model polymer systems which are of fundamental
importance in understanding the transport mechanisms. and are crucial parameters for
device development. A modified scanning photocurrent contrast microscopy technique
was designed and implemented for these studies. Patterned device substrates with
dimensions over a large range (1 μm to 2 mm) were used in these experiments. This
approach essentially utilized a photocurrent-contrast imaging of the polymer film
sandwiched between the patterned substrate and a top Schottky-type electrode, where the
incident light beam scans regions beyond the uniform electric field region of the
overlapping electrodes. The electron/hole transport processes can be independently
evaluated by positioning the narrow-light beam selectively over the anode/cathode
regions, enabling the estimation of the efficacy of hole transport vis-à-vis electron
transport. Sizable photocurrent-signals between the electrodes are observed even at
lateral distances several microns away from the counter electrode. While this current in
general decays monotonically as a function of distance from the counter electrode, the
functional forM.S. depends on the specific microscopic properties of the polymer
semiconductor, hence the method is particularly suited to directly estimate the degree of
disorder and spatial anisotropy in the electrical transport parameters. These length scales
in the first approximation corresponds to the mobility-lifetime product (μτ). The values
of these intrinsic parameters are extracted for variety of semiconducting polymers
(poly(3-hexylthtiophene)(P3HT), Poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene
vinylene) (MEHPPV) and Poly(9,9-dioctylfluorene-alt-bithiophene) (PFO-TT)). The
implications of these results are discussed in detail in the thesis.
An outcome of the studies led to the explanation of lateral photovoltaic (LPV)
effect observed in these systems.. LPV is observed using a local optical probe on device
structures consisting of the semiconducting polymer film with a Schottky type back
contact and a front pair of ohmic contacts. The measurements carried out for a large
range of interelectrode length ranging from 25 μm to 2 cm is studied in detail as a
function of temperature, wavelength, and modulation frequency of the photoexcitation. A
spreading impedance approach in the context of a discrete circuit element model is used
to obtain a quantitative understanding of the spatial dependence and the frequency
response of the LPV. |
en_US |
dc.language.iso |
English |
en_US |
dc.publisher |
Jawaharlal Nehru Centre for Advanced Scientific Research |
en_US |
dc.rights |
© 2007 JNCASR |
en_US |
dc.subject |
Semiconducting polymers |
en_US |
dc.subject |
Microscopy |
en_US |
dc.title |
Studies of length scales in semiconducting polymers using scanning photocurrent contrast microscopy |
en_US |
dc.type |
Thesis |
en_US |
dc.type.qualificationlevel |
Doctoral |
en_US |
dc.type.qualificationname |
Ph.D. |
en_US |
dc.publisher.department |
Chemistry and Physics of Materials Unit (CPMU) |
en_US |