Organic Chromophores Based on a Fused Bis-Thiazole Core and Their Application in Dye-Sensitized Solar Cells

Four new D-?-A organic dyes incorporating either a thiazolo[5,4-d]thiazole bicyclic system (TTZ1-2) or a benzo[1,2-d:4,5-d?]bisthiazole tricyclic unit (BBZ1-2) have been synthesized and fully characterized. The key steps of the synthesis include an efficient MW-assisted preparation of the thiazolo[5,4-d]thiazole core and selective functionalization of two different dihalothienyl derivatives through Suzuki coupling. All the compounds showed photo- and electrochemical properties compatible with their employment in dye-sensitized solar cells. In addition, their electronic structure and transitions were investigated by means of TD-DFT calculations. Dye-sensitized solar cells fabricated with dye TTZ1 yielded an average power conversion efficiency corresponding to 43 and 60 % of the performances recorded under the same conditions for cells containing reference dyes N3 and D5, respectively. Efficiency measurements and electrochemical impedance spectroscopy (EIS) experiments indicated that use of chenodeoxycholic acid (CDCA) as a co-adsorbent was beneficial to disrupt dye-dye interactions and slow down recombination processes within the cells, thus allowing power conversion efficiencies up to 3.53 % to be obtained.