Recent developments in solid-state dye-sensitized photovoltaic devices based on spiro-MeOTAD

The photovoltaic performance of solid-state dye-sensitized solar cells based on spiro-MeOTAD (2,2'7,7'-tetrakis(N,N-di-p-methoxyphenyl-amine)-9,9'-spirobifluorene) has been improved to 3.2% overall conversion efficiency under air mass AM 1.5 illumination by performing the dye adsorption in the presence of silver ions in the dye solution. Different spectroscopic methods, such as X-ray photoelectron, Fourier-transform infrared and UV-visible spectroscopy have been employed to scrutinize the impact of the silver on the dye-sensitized device. From spectroscopic evidence it is inferred that the silver binds to the sensitizer mainly via the amphidentate thiocyanate, allowing the formation of ligand-bridged dye complexes. The enhancement in overall device efficiency is a result of increased open circuit potential and short circuit current. The increased open circuit voltage was explained by the blocking of the dark current as a result of a closer packed dye layer and/or the partial formation of a dye double layer upon silver coordination. The increased short circuit current corresponds to the higher amount of ruthenium dye units adsorbed to the TiO 2 surface.