NIR-absorbing heptamethine dyes with tailor-made counterions for application in light to energy conversion.

A method to exchange the counterion of cyanine dyes to Δ-TRISPHAT(-) and PF6(-) is presented. The influence of these counterions on the photophysical and electrochemical properties of the cyanine dye in solution is discussed, and tendencies in the solid packing are highlighted by X-ray crystal structures. The compounds were applied in semitransparent bilayer organic solar cells together with C60, and a power conversion efficiency of 2.2% was achieved while maintaining a high transparency level in the visible region of 66%.