The relationship between squaraine dye surface morphology and sensitization behavior on SnS2 electrodes

Bis(4-dirnethylamino-2-dihydroxyphenyl)squarine (1-1 OHSQ) dyes were deposi ted on van der Waals surfaces of SnS2 single crystals by two methods, dippi ng in a dye solution and evaporation of dye solution. Dye morphologies and photosensitization properties on the same samples were studied with atomic force microscopy (AFM) and photoelectrochemical measurements. AFM experimen ts in air revealed two distinct morphologies of dye aggregates and photocur rent measurements on the same samples in aqueous electrolytes showed corres pondingly different photocurrent spectra. Three-dimensional needle-shaped 1 -1 OHSQ aggregates aligned along crystal directions and showed a broad exci tation spectrum that extended into the near-IR region with a peak around 80 0 nm. In contrast, flat aggregates presumably consisting of monolayers of 1 -1 OHSQ molecules, had a sensitization maximum around 680 nm. Both peaks we re red-shifted from absorption peak of 1-1 OHSQ in bulk dichloromethane sol ution. Spectral differences between these dye aggregates are discussed in t erms of intermolecular interactions. (C) 2000 Elsevier Science Ltd. All rig hts reserved.