| Abstract
| - Dye-sensitized solar cells (DSCs) based on nanocrystalline TiO2 have been fabricated with an amphiphilicruthenium sensitizer NaRu(2,2‘-bipyridine-4-carboxylic acid-4‘-carboxylate)(4,4‘-dinonyl-2,2‘-bipyridine)(NCS)2, coded as Z-907, and a series of ω-guanidinoalkyl acids as coadsorbents. The addition of guanidinoalkylacids as coadsorbents increased the open-circuit voltage of the DSCs and had no adverse effect on thephotocurrent if an appropriate amount was used. Phototransient measurements showed that the addition ofthese guanidino coadsorbents slowed down the charge recombination and that the increase in the open-circuitvoltage was due to suppression of the recombination or an upward shift of the TiO2 band-edge to negativepotentials. Thus, for the first time, a class of coadsorbents has been demonstrated to not only shield thesurface electrons against recombination but also to shift the band edge to negative potentials, which is essentialfor future improvements in the performance of DSCs.
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