The elaborate selection of diverse π-conjugated segments which bridge the electron donors and acceptors in organic push-pull dyes can not only tune the molecular energy-levels but also impact the interfacial energetics and kinetics of dye-sensitized solar cells (DSCs). In this paper, a series of triphenylamine-cyanoacrylic acid photosensitizers is reported with TT, EDOT-BT, EDOT-CPDT, and CPDT-EDOT (herein TT, EDOT, BT, and CPDT denote terthiophene, ethylenedioxythiophene, bithiophene, and cyclopentadithiophene, respectively) as the π-linkers, and the dye-structure correlated photocurrent and photovoltage features of DSCs based on a cobalt electrolyte are scrutinized via analyzing light absorption and multichannel charge transfer kinetics. Both stepwise incorporation of more electron-rich blocks and rational modulation of connection order of dissimilar segments can result in a negative movement of ground-state redox potential and a red-shift of the absorption peak. While these styles of reducing energy-gap do not exert too much influence on the electron injection from photoexcited dye molecules to titania, the dyestuff employing the EDOT-BT linker presents a faster interfacial charge recombination and a slower dye regeneration, accounting for its inferior cell efficiency of 5.3% compared to that of 9.4% at the AM1.5G conditions achieved by the CPDT-EDOT dye.

The judicious design of 3D giant organic dye molecules to enable the formation of a porous photoactive layer on the surface of titania is one of the viable tactics to abate the adverse interfacial charge recombination in dye-sensitized solar cells (DSCs) employing outer-sphere redox couples. Here 2′,6′-bis(octyloxy)-biphenyl substituted dithieno[3,2-b:2′,3′-d]pyrrole segment is constructed and employed as the π-linker of a high molar absorption coefficient organic push-pull dye. With respect to its congener possessing the hexyl substituted dithieno[3,2-b:2′,3′-d]pyrrole linker, the new dye can self-assemble on the surface of titania to afford a porous organic coating, which effectively slow down the kinetics of charge recombination of titania electrons with both outer-sphere tris(1,10-phenanthroline)cobalt(III) ions and photooxidized dye molecules, improving the cell photovoltage. In addition, the diminishments of charge recombination via modulating the microstructure of interfacial functional zone can also overcompensate the disadvantageous impact of reduced light-harvesting and evoke an enhanced photocurrent output, bringing forth an efficiency improvement from 7.5% to 9.3% at the 100 mW cm⁻², simulated AM1.5 conditions.