Thiocyanate-Free Ru(II) Sensitizers with a 4,4-Dicarboxyvinyl-2,2-bipyridine Anchor for Dye-Sensitized Solar Cells
A new class of thiocyanate-free Ru(II) sensitizers with 4,4-dicarboxyvinyl-2,2-bipyridine anchor and two trans-oriented pyrid-2-yl pyrazolate (or triazolate) functional chromophores is synthesized, characterized, and evaluated in dye-sensitized solar cells (DSCs). Despite their enhanced red response and absorptivity when compared to the parent sensitizer TFRS-2 that possesses standard 4,4-dicarboxyl-2,2-bipyridine anchor and shows the best conversion efficiency of = 9.82%, the newly synthesized carboxyvinyl-pyrazolate sensitizers, TFRS-11TFRS-13, exhibit inferior performance characteristics in terms of short-circuit current density (JSC), open-circuit voltage (VOC), and power conversion efficiency (), the latter being recorded to be in the range 5.607.62%. The reduction in device efficiencies is attributed to a combination of poor packing of these sensitizers on the TiO2 surface and less positive ground-state oxidation potentials, which, respectively, increase charge recombination with I3 in electrolytes and impede the regeneration of sensitizers by I anions. The latter obstacle can be circumvented in part by the replacement of the pyrazolates with triazolates, forming the TFRS-14 sensitizer, which exhibits an improved JSC, VOC, and of 16.4 mAcm2, 0.77 V, and 9.02%, respectively.