Solar Cells Based on Cyanine and Polymethine Dyes

As an alternative to heavy metal-based bipyridyl complexes, organic dyes have been studied as sensitizer in dye-sensitized nanocrystalline TiO₂ solar cells (DSSCs), among which cyanine and polymethine dye is a very important class. Remarkable progress has been made for cyanine and polymethine dyes sensitized solar cells in recent years. The formation of H- and J-aggregation of cyanine and polymethine dyes on TiO₂ surface significantly widens the absorption spectra and photoaction spectra of DSSCs in the visible spectra. The structure of cyanine and polymethine dyes affects the adsorption amount on TiO2 electrode and therefore affects the performance of the solar cells. The dyes with highest occupied molecular orbital (HOMO) level make it possible to use 4-tert-butylpyridine to improve the open circuit voltage of DSSCs. The highest overall conversion efficiency of DSSCs based on cyanine and polymethine dyes has reached 7.7%. The potential use of cyanine dyes in thin-film heterojunction all-organic photovoltaic devices has also been investigated.