Dye-sensitized solar cells based on D—A—π—A′ structures with a 4H-cyclopenta[2,1-b:3,4-b′]dithiophene fragment containing branched alkyl groups

Two new dyes were obtained; their D—A—π—A′ structure included benzo[d][1,2,3]-thiadiazole as an internal acceptor (A), a cyanoacrylic acid residue as a terminal anchor acceptor (A′), a 4H-cyclopenta[2,1-b:3,4-b′]dithiophene π-spacer with branched alkyl groups, and 2,3-dihydroindole condensed with carbocycles as a donor. The optical and electrochemical characteristics of the obtained dyes were determined, and solar cells based on them were assembled. The power conversion efficiency reached 3.05% for a device based on the dye containing a 2,3,4,4a,9,9a-hexahydro-1H-carbazole donor moiety. The relatively low value of photovoltaic efficiency is likely due to excessive steric effects that are demonstrated by the branched alkyl groups when the dyes are sorbed onto the TiO₂ surface, which leads to an insufficient concentration of the dye on the electrode surface, resulting in a decrease in the quantity of absorbed photons.