N-Alkyl- and N-aryl-dithieno[3,2-b:2′,3′-d]pyrrole-containing organic dyes for efficient dye-sensitized solar cells

Two new organic sensitizers, 2-cyano-3-(6-(4-(diphenylamino)phenyl)-4-(2-ethylhexyl)-4H-dithieno3,2-b:2′,3′-d]pyrrol-2-yl)acrylic acid and 2-cyano-3-(6-(4-(diphenylamino)phenyl)-4-(4-(hexyloxy)phenyl)-4H-dithieno3,2-b:2′,3′-d]pyrrol-2-yl)acrylic acid, consisting of electron donating (triphenylamine) and electron accepting (cyanoacrylic acid) functionalities linked by two different rigidified π-spacers, N-alkyl- and N-aryl-dithieno3,2-b:2′,3′-d]pyrrole, were designed, synthesized and applied for dye-sensitized solar cells, respectively. The materials were successfully synthesized through Knoevenagel condensation reactions. Ultraviolet–visible absorption spectra revealed that the use of either of rigidified π-spacer resulted in similar charge transfer transition, however, enhanced spectral response was observed when compared with an oligothiophene analogue. In terms of their photovoltaic performance, new dyes outperformed the reference bithiophene sensitizer when tested with nitrile-based and ionic liquid-based electrolytes.