Effect of structural optimization on the photovoltaic performance of dithieno[3,2-b:2′,3′-d]pyrrole-based dye-sensitized solar cells

Abstract

Five novel organic push–pull dyes, DT, CD-T, TD-T, CD-C and TD-P, based on carbazole or triphenylamine as donors, dithieno[3,2-b:2′,3′-d]pyrrole as a π-spacer and cyanoacetic acid as an acceptor were synthesized, and their structures were optimized for DSSCs. Dithieno[3,2-b:2′,3′-d]pyrrole was linked with either carbazole or triphenylamine via a Suzuki coupling reaction. Followed by formylation via a Vilsmeier–Haak reaction, and then a Knoevenagel condensation reaction was employed to link cyanoacetic acid, producing the carbazole-based dyes CD-C and CD-T and the triphenylamine-based dyes TD-P and TD-T. Meanwhile, the dye DT was synthesized as a reference for comparison. The molar extinction coefficients of the carbazole-based dyes CD-T and CD-C were 56 370 M⁻¹ cm⁻¹ and 62 471 M⁻¹ cm⁻¹, while those of the dyes based on triphenylamine, TD-T and TD-P, were 44 555 M⁻¹ cm⁻¹ and 49 945 M⁻¹ cm⁻¹, respectively. The optimized power conversion efficiency of CD-T reached 6.63% with an open-circuit voltage of 710 mV, a short-circuit current density of 14.55 mV cm⁻², and a fill factor of 0.64.