Metal-Free Sensitizers with a Perfluorohexyl Side Chain for Dye-Sensitized Solar Cells: Properties Alien to Alkyl Chains

New fluorene dyes containing a perfluorohexyl or an n-hexyl side chain in the conjugated spacer (thiophene) were synthesized for application in dye-sensitized solar cells. The perfluoro dyes more effectively suppress the charge recombination than their congeners containing a hexyl chain, which leads to a higher open-circuit voltage (V_OC). The more efficient dark current suppression afforded by the perfluorohexyl-containing dyes was also confirmed by electrochemical impedance spectroscopy. A perfluoro-containing dye exhibited the best power conversion efficiency of the synthesized compounds, which was further improved to 6.73 % by the addition of chenodeoxycholic acid (10 mm) as a co-adsorbant. The hydrophobic perfluorohexyl-containing dyes are more resistant to leaching due to the presence of moisture, leading to higher temporal stability of the DSSCs.