Judicious design of L(D-π-A)2 type di-anchoring organic sensitizers for highly efficient dye-sensitized solar cells: Effect of the donor-linking bridges on functional properties

Construction of di-anchoring organic sensitizers has been recently recognized as an effective strategy to develop high-efficiency dye-sensitized solar cells (DSSCs). However, the relatively low open-circuit photovoltage (V-oc) for di-anchoring dyes have become to be the bottle-neck for further advancing the photovoltaic performance. In this work, two novel L(D-pi-A)(2) type di-anchoring sensitizers, W11-W12, featuring 9H-thieno[2',3':4,5]thieno [3,2-b]thieno[2',3':4,5]thieno[2,3-d]pyrrole (TTTP) as pi-conjugated spacer, have been developed and well examined for a systematical study of the structure-property relationship of these dyes. Through the rational adjustment of donor-linking bridges, carbazole decorated W12 exhibits dramatically enhanced light-harvesting efficiency as well as self-anti-aggregation ability with respect to those of W11 employing triphenylamine linkage. More importantly, a compact arranged organic layer benefiting from the superior dye-loading amounts has been formed for W12, which is beneficial to keep the oxidized electrolyte from the TiO2 surface, thus bringing forth more efficient suppression of interfacial charge recombination and consequently higher V-oc values. Under standard AM 1.5 G illumination, DSSCs sensitized by W12 employing [Co(phen)(3)](2+/3+) electrolyte display a fascinating power conversion efficiency as high as 8.28%, with an impressive open-circuit voltage (V-oc) of 847 mV, which is among the highest cells efficiencies of L(D-pi-A)(2) type di-anchoring organic dyes.