Abstract Donor-π-acceptor YD2-o-C8, WW-6, and SM315 are among best-performing Zn-porphyrins for their outstanding light-harvesting properties. To reach the further enhancement of photovoltaic performance of the corresponding cells, co-sensitization of these typical porphyrins with those dyes possessing intense absorption in the green spectral region (typically, Y123) is necessary. In this work, using density functional theory (DFT) and time-dependent DFT (TD-DFT) approaches, co-sensitization mechanism in the above three typical Y123/Zn-porphyrin systems has been systematically investigated. Moreover, due to the excellent performance of dithienosilole (DTS) group in organic dyes, it is designed here to replace the benzothiadiazole (BTD) unit in SM315 to give a new Zn-porphyrin dye designated SM315-1. This specific modification of SM315 can effectively retard the interfacial charge recombination compared to that in YD2-o-C8 and WW-6 cells by reducing the contact between oxidized porphyrins and injected electrons in TiO2 substrate, and simultaneously improves the overall light harvesting ability of the co-sensitized film with the theoretical maximum limit of photocurrent to be 38.31 mA/cm2. The both favorable aspects suggest an attractive application of the fully novel Y123/SM315-1 co-sensitized film in dye-sensitized solar cell (DSSC).