Date of Award

12-31-2015

Document Type

Campus Access Thesis

Degree Name

Master of Science (MS)

Department

Chemistry

First Advisor

Jonathan Rochford

Second Advisor

Jason Evans

Third Advisor

Michelle Foster

Abstract

Dye-sensitized solar cells (DSSCs) have seen an influx of research since Grätzel’s seminal 1991 Nature paper. Although easier to fabricate and cheaper to produce, their commercial viability depends on reaching power conversion efficiencies on par with current photovoltaic technologies such as silicon thin film solar cells. This thesis contributes to the growing library of new redox mediators and light-absorbing photosensitizers as pathways to improved DSSC performance. Following a thorough review of DSSC technologies and advancements in Chapter 1, Chapter 2 introduces a novel cobalt(III/II) redox mediator, [Co(bpq)2]3+/2+ (bpq = 2,6-bis(8-quinolinyl)pyridine) and compares its performance to [Co(tpy)2]3+/2+ (tpy = 2,2’:6’,2’’-terpyridine). Electrochemical impedance studies (EIS) of symmetric cells as well as functional DSSC devices are presented. These studies suggest that the [Co(bpq)2]3+/2+ redox system suffers decreased turnover at the counter electrode and increased mass-transfer resistance resulting in a slight decrease in power conversion efficiency (PCE) from η = 4.47% to η = 3.73% when compared to the [Co(tpy)2]3+/2+ redox system. Chapter 3 explores the non-innocent ligand bonding effect of π-donating β-diketonate ligands on the ruthenium bis-bipyridine metal complex. [Ru(bpy)2(β-diketonate)]+ complexes, where bpy = 2,2’-bipyridine and β-diketonate = acetylacetone (acac); 1,3-diphenyl-1,3-propanedione (Ph2acac); 1,7-diphenyl-1,4,6 heptadione (Ph2curc); curcumin (curc); 3-phenyl-acetylacetone (phacac); 2-roxybenzophenone (OBP); 5-oxyflavone (OFlav); and 1-coumarin-acetylacetone (coumarin-acac), vary in their symmetry and extent of π-conjugation. Computational, UV/Vis, and electrochemical data is presented and are consistent with non-innocent ligand theory, facilitated by β-diketonate ligand. Finally, [Ru(dcbpy)2(β-diketonate)]+ analogs are presented and utilized in DSSC devices displaying PCE ranging from η = 0.18% - 2.78%. The lowest PCE (η = 0.18%) observed for [Ru(dcbpy)2(Ph2acac)]+ is due to poor excited state electron delocalization. The poor PCE (η < 1%) for other [Ru(dcbpy)2(β-diketonate)]+ devices is attributed to poor dye regeneration, the result of poor energy level alignment between the HOMO and the redox potential of the I3-/I- redox mediator. However, future studies incorporating different redox mediators could significantly improve PCE for Ru(dcbpy)2(β-diketonate)]+ based DSSC.

Comments

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