Palladium-catalyzed direct arylation: organic dyes with enhanced optical properties for photovoltaic applications

Dye-sensitized solar cell (DSSC) is an emerging photovoltaic (PV) technology allowing solar light harvesting even through colored semitransparent devices, such properties better meet the architectonical requirements for the exploitation in the urban context. The core component of a DSSC is the molecular dye; new organic dyes are generally developed following the D-A-?-A structural design. Some compounds have reached outstanding PV performances at the cost of low devices transparency and complex synthesis of non-symmetric structures obtained with metalorganic cross-couplings. We recently explored new structural designs for symmetrical organic photosensitizers that can be obtained with short synthetic strategies based on Palladium-catalyzed direct arylation reactions on a thienopyrazine core. The obtained dyes feature divergent optical properties ranging from pitch dark coloration to high transparency and uncommon colorations like green tones were also obtained. In order to enhance the divergent optical properties of the dyes, the PV devices were assembled using dedicated electrolyte compositions with no effect on the coloration and thin layers of supporting semiconductors allowing for high transparency. Among the resulting DSSC full devices, some have shown a composition of the transmitted light that fits well the human eye sensitivity spectrum, satisfying the requirements of perceived transparency for Building-Integrated PV.