Metal-to-Ligand Charge Transfer (MLCT) Excited States of Ruthenium Polypyridyl Compounds Relevant to Dye-Sensitized Solar Cells (DSSCs)

ruthenium;dye-sensitized solar cell;DSSC;photochemistry;excited state relaxation;interfacial electric field;Chemistry

O'Donnell, Ryan MichaelMeyer, Gerald J. ;

Johns Hopkins University

关键词: ruthenium;    dye-sensitized solar cell;    DSSC;    photochemistry;    excited state relaxation;    interfacial electric field;    Chemistry;   

Others  :  https://jscholarship.library.jhu.edu/bitstream/handle/1774.2/39337/ODONNELL-DISSERTATION-2015.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: JOHNS HOPKINS DSpace Repository

【 摘 要 】

Climate change is of increasing global concern and has stimulated the development of alternative renewable energy sources. Dye-sensitized solar cells (DSSCs) are a promising third generation photovoltaic technology due to their low manufacturing costs, spectral tunability, flexibility, and potential for residential and commercial building integration. DSSCs employ ruthenium polypyridyl compounds to sensitize wide-bandgap semiconductors, typically titanium dioxide, to visible light. The aforementioned topics are introduced in Chapter 1. This thesis will elucidate the fate of metal-to-ligand charge transfer (MLCT) excited states of ruthenium polypyridyl compounds both in fluid solution and anchored to mesoporous metal oxide thin films and relate the findings to DSSCs. Chapter 2 describes the excited state relaxation pathways of ruthenium polypyridyl compounds containing isothiocyanate groups. This research demonstrates that the activation energy associated with ligand loss photochemistry in fluid solution increases significantly once the compounds are anchored to TiO2 or ZrO2 thin films and helps to explain the remarkable photostability of DSSCs. Chapter 3 begins by reviewing Stark effects observed at semiconductor-sensitizer interfaces. Excited state electron injection into titanium dioxide nanocrystals generates an interfacial electric field which perturbs the MLCT excited states of surface-bound sensitizers. Experimental measurements on the charge screening of interfacial electric fields by monovalent and divalent Lewis acidic metal cations are presented. The compound [RuII(dtb)2(dcbH2)]2+, where dtb is 4,4’-di-tert-butyl-2,2’-bipyridine and dcb is 2,2’-bipyridine-4,4’-dicarboxylic acid, was used to quantify the magnitude of these fields in the presence of different cations and the charge-screening kinetics of the cations following excited state electron injection.Chapter 4 presents kinetic studies performed in the presence of the triiodide redox mediator, I3-, which provide compelling evidence that the anionic nature of I3- inhibits unwanted charge recombination in DSSCs.Chapter 5 presents the excited state acid-base reactions of [RuII(dtb)2(dcbH2)]2+ and [RuII(btfmb)2(dcbH2)]2+, where btfmb is 4,4’-bis(trifluoromethyl)-2,2’-bipyridine. Although the protonatable ligand, dcbH2, was identical for both compounds, it was found that the ancillary ligands could tune the excited state to be either more acidic (pKa* = 2.0 for btfmb) or basic (pKa* = 3.8 for dtb) than the ground state (pKa = 2.9 for both compounds).