Tuning the Properties of Isoindigo-Based Organic Semiconductors Through Structural Engineering
| dc.contributor.advisor | Kelly, Timothy L | |
| dc.contributor.committeeMember | Gravel, Michel | |
| dc.contributor.committeeMember | Steer, Ronald P | |
| dc.contributor.committeeMember | Chang, Gap Soo | |
| dc.contributor.committeeMember | Sanders, David | |
| dc.creator | Randell, Nicholas M. 1990- | |
| dc.creator.orcid | 0000-0001-9408-3510 | |
| dc.date.accessioned | 2017-12-01T19:43:55Z | |
| dc.date.available | 2018-12-01T06:05:10Z | |
| dc.date.created | 2017-11 | |
| dc.date.issued | 2017-12-01 | |
| dc.date.submitted | November 2017 | |
| dc.date.updated | 2017-12-01T19:43:55Z | |
| dc.description.abstract | Solar power is one of the most prominent renewable energy technologies vying to replace fossil fuels. Traditionally, this field has been dominated by silicon solar cells; recent innovations, such as organic photovoltaic devices (OPVs), offer the possibility of lightweight, flexible solar power generation with a wide range of applications, from building façades to textiles. Unfortunately, organic solar cells suffer from low power conversion efficiencies. To overcome this problem, the design of new organic semiconductors has become an area of intense research. In engineering these materials, it is essential to develop strong links between molecular structure and the optoelectronic properties of the resulting semiconductors, such as optical band gap, extinction coefficient, frontier orbital energies, and charge carrier mobility. This thesis explores the relationship between structural differences in isoindigo derivatives, such as increasing electron deficiency, or increased molecular planarity, and differences in the resulting material’s optoelectronic properties. The first two sections of this thesis investigate the effects of heteroatom substitution on isoindigo-based semiconductors. Four target compounds were synthesized, each containing either electron-withdrawing nitrogen atoms, or electron rich alkoxy groups. The semiconductors were incorporated into the active layer of organic solar cells. Alkoxy substitution was shown to improve device efficiency; conversely, nitrogen substitution led to lowered device efficiency. In a follow-up study, it was shown that the azaisoindigo groups were capable of coordinating to a Lewis acid; this coordination caused a red-shift in the molecule’s S0S1 transition. The Lewis adduct was identified using UV/vis spectroscopy, NMR spectroscopy, and (TD)DFT calculations. It was then demonstrated that the coordination reaction could be performed with vapor phase Lewis acids. The third project in this thesis focuses on the synthesis of two isoindigo dimers. The first, bisisoindigo, is a ring-fused dimer of isoindigo. This was chosen to study the effects of increased planarity and conjugation length on the optoelectronic properties of isoindigo. Initially, both bisisoindigo and a donor-acceptor molecular semiconductor based on bisisoindigo were synthesized, characterized, and used in OPVs. Poor active layer morphology, due to aggregation of the bisisoindigo, led to low efficiencies in the OPVs. Following work on the ring-fused isoindigo structure, a second dimer was synthesized in which two isoindigo units were joined by a single bond; this design provides free rotation between isoindigo units. Both dimers, as well as isoindigo, were used as electron acceptors in a study of the effects of acceptor number and planarity in donor-acceptor copolymers. The acceptors were copolymerized with thiophene and terthiophene to yield a total of six polymers. Both the optoelectronic properties of these polymers, and their performance in OPVs, were compared to discover trends in donor-acceptor semiconductor properties with increasing acceptor content. Over the course of four major projects it has been demonstrated that altering the structure of the conjugated building block isoindigo has major effects on the optical band gap, orbital energies, and charge transport characteristics of the resulting organic semiconductors. The final chapter of this thesis will serve to link these projects in a general discussion of how the design of isoindigo-based organic semiconductors can be used to produce desired optoelectronic properties in the resulting materials. The thesis will conclude with a brief look towards the prospects of this area of research, including establishing the general applicability of these design strategies to organic semiconductors beyond those based on isoindigo. | |
| dc.format.mimetype | application/pdf | |
| dc.identifier.uri | http://hdl.handle.net/10388/8289 | |
| dc.subject | Organic solar cells, isoindigo, materials chemistry | |
| dc.title | Tuning the Properties of Isoindigo-Based Organic Semiconductors Through Structural Engineering | |
| dc.type | Thesis | |
| dc.type.material | text | |
| local.embargo.terms | 2018-12-01 | |
| thesis.degree.department | Chemistry | |
| thesis.degree.discipline | Chemistry | |
| thesis.degree.grantor | University of Saskatchewan | |
| thesis.degree.level | Doctoral | |
| thesis.degree.name | Doctor of Philosophy (Ph.D.) |