Organic sensitizers featuring 9H-thieno[2′,3':4,5]thieno[3,2-b]thieno[2′,3':4,5]thieno[2,3-d]pyrrole core for high performance dye-sensitized solar cells

Judicious design alkyl side chain decorated fused aromatic heterocycles as π-spacers has proved to be an efficient strategy to construct highly efficient organic sensitizers. Three novel metal-free dyes W02–04 featuring a highly planar and extensively conjugated 9H-thieno[2′,3':4,5]thieno[3,2-b]thieno[2′,3':4,5]thieno[2,3-d]pyrrole (TTTP) π-bridge have been successfully constructed and applied in dye-sensitized solar cells (DSSCs) for the first time. To better understand the TTTP bridge, the dye W01 possessing the nonplanar 3-hexylthiophene-dithieno[3,2-b:2′,3′-d]pyrrole-3-hexylthiophene linker is prepared as a reference. Introduction of TTTP bridge into the dyes skeleton notably enhances the molar extinction coefficients (ε) by comparison with the reference dye, and much improved short-circuit current (Jsc) have been realized. Meanwhile, dynamics measurements reveal that the charge recombination in devices has been significantly reduced by the incorporation of TTTP bridge. Among these dyes, the DSSCs fabricated with W03 employing cobalt electrolyte achieves an excellent power conversion efficiency of 9.43%, with open-circuit voltage (Voc) of 848 mV, Jsc of 16.2 mA cm−2, and fill factor of 0.70 under simulated AM 1.5 G conditions. This work provides important new insight into designing novel organic sensitizers with high ε and efficient suppression of charge recombination.