Bis(Tridentate) Cycloruthenated Sensitizers for the Dye-Sensitized Solar Cell.

摘要

A series of bis(tridentate) cycloruthenated complexes have been synthesized and characterized for the dye-sensitized solar cell (DSSC). The title cycloruthenated complexes exhibit broader absorption profiles and cathodically shifted Ru(III)/Ru(II) redox potentials relative to their polypyridyl congeners. It is shown herein that derivatives of [Ru(tpy)(pbpy)] + and [Ru(tpy)(dpb)]+ (tpy = 2,2':6',2''-terpyridine; pbpy = 6-phenyl-2,2'-bipyridine; dpb = 1,3-bis(2-pyridyl)benzene)), in particular, display a range of properties that enable high performance in the DSSC and offer insight into fundamental processes related to the sensitization of TiO2.;This dissertation also documents how the light absorbing properties of [Ru(tpy)(pbpy)]+ complexes can be dramatically increased through the installation of a secondary organic triphenylamine (TPA) chromophore. These bichromic cycloruthenated complexes exhibit a broad (400-800 nm) and intense (epsilon up to 64.0 x 103 M-1 cm-1) absorption envelope throughout the visible spectrum, and can reach power-conversion efficiencies (PCE) as high as 8.02% (polypyridyl derivatives cannot achieve PCEs higher than 1%!).;Modification of the TPA and anionic ring of the pbpy chelated with electron-donating groups (EDGs) and electron-withdrawing groups (EWGs) enables the independent modulation of the Ru(III)/Ru(II) and TPA•+/TPA 0 redox potentials over 180 and 230 mV, respectively. The ability to tune each of the redox potentials independently results in acute synthetic control of the location of the highest-occupied molecular orbital (HOMO). This unique property offers the opportunity to turn on and off an intramolecular hole-transfer (after light-induced charge-transfer into TiO2) by confining the HOMO to the TPA or the metal chromophore, respectively. The interrogation of these dyes on the surface revealed many interesting features, including the open-circuit voltage (VOC) of the cell being acutely sensitive to the spatial proximity of the hole to the TiO 2 surface.;Metal-free organic sensitizers derived from ligand precursors, were synthesized to include S or O atoms on TPA and studied to directly probed the dye regeneration step. Our hypothesis that the soft polarizable sulfur atom would facilitate regeneration of the oxidized dye by the soft, polarizable I- ion was confirmed by transient absorption spectroscopy data: the sulfur-containing dye regenerated 25-fold faster the oxygen derivative. Tailoring the dye to facilitate regeneration results in improved PCEs. This work is important in that it provides atomic level resolution of how to prepare DSSC dyes.