Toward Optimization of Oligothiophene Antennas: New Ruthenium Sensitizers with Excellent Performance for Dye-Sensitized Solar Cells

Abstract

This paper reports on the design and synthesis of three new ruthenium sensitizers, as well as the optimization of their linear or dendritic light-harvesting oligothiophene antennas to achieve superior device performance. The three new ruthenium sensitizers, [Ru(dcbpy)(obtip)(NCS)2] (JF-5, dcbpy =4,4′-dicarboxylic acid-2,2′-bipyridine, obtip =2-(5-octyl-(2,2′-bithiophen)-5′-yl)-1H-imidazo[4,5-f][1,10]phenanthroline), [Ru(dcbpy)(ottip)(NCS)2] (JF-6, ottip =2-(5-octyl-2,2′,5′,2′′-terthiophen)-5′′-yl)-1H-imidazo[4,5-f][1,10]phenanthroline), and [Ru(dcbpy)(dottip)(NCS)2] (JF-7, dottip =2-(2,3-di-(5-octylthiophen-2-yl)thiophen-5-yl)-1H-imidazo[4,5-f][1,10]phenanthroline), were synthesized in a typical one-pot reaction. The ruthenium sensitizer JF-5 incorporating a linear and planar 2,2′-bithiophene antenna showed the best DSCs performance (9.5%; compared to N3, 8.8%). The difference in the performance of these sensitizers demonstrates that elongating the linear and planar light-harvesting antenna result in an enhancement in MLCT intensity, but a reduction in the quantity of dye-loading. This finding not only permitted the power-conversion efficiency in ruthenium sensitizers containing oligothiophene antennas to be optimized, but also points to a promising direction for molecule engineering in DSCs.