Carbazole-based twin molecules as hole-transporting materials in dye-sensitized solar cells

Three new carbazole-based twin molecules with non-conjugated linear alkyl chains of various length as linker were synthesized in a one-step reaction. The new hole-transporting materials TCz-C3, TCz-C6, and TCz-C12 exhibit molecular glass behavior and the glass transition temperature can be tuned via the length of the linker. The optical and electrochemical properties are not significantly altered by the twin molecular structure, while the glass transition temperature increases and the hole mobility is strongly increased with reduced chain length by up to almost one order of magnitude, as determined from OFET measurements in saturation regime, demonstrating that conjugated linkers are not necessarily required in the design of twin molecules. The molecule with the shortest chain length (C-3), namely TCz-C3, exhibited a promising power conversion efficiency of 2.21% in solid-state DSSC using the D102 dye as organic sensitizer.