Four thiocyanate-free ruthenium sensitizers (DUY24-DUY27) containing 2-thienylpyridine moiety as cyclometalating core were synthesized for dye-sensitized solar cell (DSC) application. To the best of our knowledge, DUY24-DUY27 are four best-efficiency sensitizers having 42%-65% higher efficiencies compared to those of the published sensitizers comprising the same type of the cyclometalating ancillary ligands. The significant characteristic of DUY24-DUY27 is their β-lowest unoccupied spin orbital (β-LUSO) distributes remarkably on the cyclometalating ligands, especially on the soft sulfur atom, which strengthens the interaction between the oxidized dye and iodide ion for efficient dye regeneration. The photovoltaic performance of DUY24-DUY27-based DSCs supports that the dye regeneration (therefore the short-circuit photocurrent density (JSC) of the cell) can be improved by not only lowering the highest occupied molecular orbital energy level of the dye molecule but also distributing the β-LUSO properly on the soft atoms. The study provides an important new guide for designing high-efficiency ruthenium-based dyes for DSC application.