Aggregation behavior of differently substituted Ru(II)-complex dyes as sensitizers for electrodeposited ZnO solar cells

Properties of newly developed Ru(II)-complex dye, cis -bis(isothiocyanato) (2,2′-bipyridyl-4,4′-dicarboxylato) ( N -(4-butoxyphenyl)- N -2-pyridinyl-2-pyridinamine)-ruthenium(II) (J13), having a triarylamine ligand have been studied in comparison with cis -bis(isothiocyanato) bis(2,2′-bipyridyl-4,4′-dicarboxylato)-ruthenium(II) (N3), as photosensitizers for solar cells employing electrodeposited porous ZnO thin films. Quantification of dye loading as well as change of the film morphology on extension of the soaking time in solutions of these dyes indicated spontaneous monolayer formation of the J13 dye, in contrast to the strongly aggregating N3 dye. Overloading of the N3 dye molecules not directly bound to ZnO caused decreased J sc as well as worsening of F.F. , so that the efficiency of the N3 cell created a peak with a moderate dipping time. On the other hand, the efficiency of the J13 cells simply saturated to a value of ca. 4% as the dye monolayer was formed, indicating its better chemical match with ZnO.