Developing Structural Probes for Designed Molecular Architectures
Author(s)
James, David Thomas
Type
Thesis
Abstract
This thesis is concerned with the development of techniques to probe and control molecular
morphology in organic semiconductors and investigate structure-property relationships.
An angle-dependent polarised Raman technique is developed to probe molecular order and
orientation in 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) thin lms, and
applied to understand the role of blending with polystyrene on morphology and charge transport
properties in inkjet-printed organic field-effect transistors (OFETs). Compared to pristine
devices, blending improves film uniformity in terms of device coverage and molecular orientation
and increases saturation mobility from [Mathematical formula appears here. To view, please open pdf attachment].
A zone-casting apparatus is developed to systematically control the grain size and molecular
orientation of TIPS-pentacene thin films. Processing parameters such as solvent, solution
temperature, substrate temperature and casting speed are systematically controlled to study film coverage, grain size, alignment and orientation, and applied to investigate charge transport
properties in TIPS-pentacene and 6,13-bis(triethylsilylethynyl) pentacene (TES-pentacene)
OFETs. Casting speed and grain orientation strongly influence device performance. TIPS-
pentacene shows higher mobilities and grain-boundary-limited transport while TES-pentacene
charge transport is limited by crystal orientation.
The anisotropic structural and optical properties of TIPS-pentacene and TES-pentacene films are characterised using polarised UV-visible absorption and Raman spectroscopy. Evidence for
J- and H-aggregation is found from a packing-induced red-shifted and blue-shifted absorption
transition, respectively. Angle-dependent polarised Raman spectroscopy is used to probe the
molecular orientation and order in the films. The pentacene long-axis orientation is found to
be ±(50-60)° relative to the zone-casting direction for both materials, while TIPS-pentacene
shows a higher Raman anisotropy than TES-pentacene.
Quantum-chemical studies are performed on a range of conjugated polymer systems. Using
simulated structure-property relationships, the effect of side chain placement & positioning,
blending with small molecules, thermal annealing and heavy-atom substitution on the opto-
electronic and charge transport properties of the polymers are discussed.
morphology in organic semiconductors and investigate structure-property relationships.
An angle-dependent polarised Raman technique is developed to probe molecular order and
orientation in 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) thin lms, and
applied to understand the role of blending with polystyrene on morphology and charge transport
properties in inkjet-printed organic field-effect transistors (OFETs). Compared to pristine
devices, blending improves film uniformity in terms of device coverage and molecular orientation
and increases saturation mobility from [Mathematical formula appears here. To view, please open pdf attachment].
A zone-casting apparatus is developed to systematically control the grain size and molecular
orientation of TIPS-pentacene thin films. Processing parameters such as solvent, solution
temperature, substrate temperature and casting speed are systematically controlled to study film coverage, grain size, alignment and orientation, and applied to investigate charge transport
properties in TIPS-pentacene and 6,13-bis(triethylsilylethynyl) pentacene (TES-pentacene)
OFETs. Casting speed and grain orientation strongly influence device performance. TIPS-
pentacene shows higher mobilities and grain-boundary-limited transport while TES-pentacene
charge transport is limited by crystal orientation.
The anisotropic structural and optical properties of TIPS-pentacene and TES-pentacene films are characterised using polarised UV-visible absorption and Raman spectroscopy. Evidence for
J- and H-aggregation is found from a packing-induced red-shifted and blue-shifted absorption
transition, respectively. Angle-dependent polarised Raman spectroscopy is used to probe the
molecular orientation and order in the films. The pentacene long-axis orientation is found to
be ±(50-60)° relative to the zone-casting direction for both materials, while TIPS-pentacene
shows a higher Raman anisotropy than TES-pentacene.
Quantum-chemical studies are performed on a range of conjugated polymer systems. Using
simulated structure-property relationships, the effect of side chain placement & positioning,
blending with small molecules, thermal annealing and heavy-atom substitution on the opto-
electronic and charge transport properties of the polymers are discussed.
Date Issued
2012-10
Date Awarded
2013-01
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Kim, Ji-Seon
Sponsor
Val O'Donoghue Scholarship in Natural Sciences ; Cambridge Display Technologies, Ltd.
Publisher Department
Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)