Post-polymerisation modification of conjugated polymers: towards novel organic semiconductor materials
File(s)
Author(s)
Rapley, Charlotte Louise
Type
Thesis
Abstract
Organic conjugated polymer semiconductor materials have grasped the attention of many
researchers, particularly in the last 10 years, for their use in electronic devices. In order to
engineer materials for specific applications, it is essential to consider the polymer design and
chemical structures. With thoughtful polymer design, it is possible to modify and manipulate
physical and optoelectronic properties to optimise semiconductor materials for intended
applications.
Post-polymerisation techniques have been widely explored as a useful tool to modify
polymers with desired properties or specialised functionality. Nucleophilic aromatic
substitution (SNAr) has been identified as a useful reaction to facilitate the modification of
conjugated polymers without introducing unwanted defects within the polymer backbone. In this thesis, SNAr was used as technique to introduce conjugated polymer sidechains and
various other functional groups along conjugated polymer backbones. Polymers were
designed and synthesised for use in electronic devices such as; organic thin-film transistors
(OTFTs) and organic solar cell (OSC) devices, where physical and optoelectronic properties
were evaluated for all polymers.
The work presented (Chapter 2-6) looks at polymers designed with a monofluorinated
benzothiadiazole as a repeat unit within the backbone of a conjugated polymer. A range of
nucleophiles were substituted onto the polymer backbones via SNAr, directly onto the
monofluorinated benzothiadiazole repeat unit, highlighting the versatility of this post-polymerisation modification method. In chapters 2 and 3, this method was used to develop graft co-polymers with an n-type conjugated polymer backbone and p-type conjugated polymer sidechains. In chapter 3, single-component graft co-polymer structures were shown to provide a comparatively similar solar cell device performance to the blended polymers, however, with higher recorded Voc values.
Further exploration of the versatility of post-polymerisation modification requires the
development of new conjugated backbone polymers that can readily undergo modification.
Hence, in Chapter 4, the direct modification of two novel n-type conjugated polymer backbones via SNAr was demonstrated, including the quantitative incorporation of
substituents along the polymer backbone. Unsubstituted polymers achieved an electron
mobility of 0.16 cm2 V-1 s-1 in OTFT devices. After substitution, mobilities reduced by around
one order of magnitude. Further developments looked at azide functionalised conjugated
polymers, where polymer thin films were successfully thermally cross-linked or photo-patterned (high azide content polymer). Finally in Chapter 5, polymers were modified with
increasing anionic content, for use as interlayers between active polymer layers and
electrodes within OSCs, for example. Increasing the anionic content did not largely affect the
electronic properties of the polymer, however, did modify the work function of indium tin
oxide (ITO).
researchers, particularly in the last 10 years, for their use in electronic devices. In order to
engineer materials for specific applications, it is essential to consider the polymer design and
chemical structures. With thoughtful polymer design, it is possible to modify and manipulate
physical and optoelectronic properties to optimise semiconductor materials for intended
applications.
Post-polymerisation techniques have been widely explored as a useful tool to modify
polymers with desired properties or specialised functionality. Nucleophilic aromatic
substitution (SNAr) has been identified as a useful reaction to facilitate the modification of
conjugated polymers without introducing unwanted defects within the polymer backbone. In this thesis, SNAr was used as technique to introduce conjugated polymer sidechains and
various other functional groups along conjugated polymer backbones. Polymers were
designed and synthesised for use in electronic devices such as; organic thin-film transistors
(OTFTs) and organic solar cell (OSC) devices, where physical and optoelectronic properties
were evaluated for all polymers.
The work presented (Chapter 2-6) looks at polymers designed with a monofluorinated
benzothiadiazole as a repeat unit within the backbone of a conjugated polymer. A range of
nucleophiles were substituted onto the polymer backbones via SNAr, directly onto the
monofluorinated benzothiadiazole repeat unit, highlighting the versatility of this post-polymerisation modification method. In chapters 2 and 3, this method was used to develop graft co-polymers with an n-type conjugated polymer backbone and p-type conjugated polymer sidechains. In chapter 3, single-component graft co-polymer structures were shown to provide a comparatively similar solar cell device performance to the blended polymers, however, with higher recorded Voc values.
Further exploration of the versatility of post-polymerisation modification requires the
development of new conjugated backbone polymers that can readily undergo modification.
Hence, in Chapter 4, the direct modification of two novel n-type conjugated polymer backbones via SNAr was demonstrated, including the quantitative incorporation of
substituents along the polymer backbone. Unsubstituted polymers achieved an electron
mobility of 0.16 cm2 V-1 s-1 in OTFT devices. After substitution, mobilities reduced by around
one order of magnitude. Further developments looked at azide functionalised conjugated
polymers, where polymer thin films were successfully thermally cross-linked or photo-patterned (high azide content polymer). Finally in Chapter 5, polymers were modified with
increasing anionic content, for use as interlayers between active polymer layers and
electrodes within OSCs, for example. Increasing the anionic content did not largely affect the
electronic properties of the polymer, however, did modify the work function of indium tin
oxide (ITO).
Version
Open Access
Date Issued
2022-02
Date Awarded
2022-05
Copyright Statement
Creative Commons Attribution NonCommercial NoDerivatives Licence
Advisor
Heeney, Martin
Sponsor
Engineering and Physical Sciences Research Council (EPSRC)
Publisher Department
Chemistry
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)