Two novel coumarin-substituted phthalocyanine dyes (CAPc and CSPc) with different linking units, using carboxylic groups as electron acceptor and injector, were designed, synthesized, and applied as panchromatic organic sensitizers in I−/I 3− -based dye-sensitized solar cells (DSSCs). The asymmetric coumarin–phthalocyanine dyad analogue (OAPc) and the symmetric coumarin-phthalocyanine dyad analogue (COPc) were also synthesized for comparison. The structure–property relationship for these dyes was investigated by absorption spectroscopy, cyclic voltammetry, and thermogravimetric analysis. The ultraviolet–visible (UV–Vis) absorption was dramatically affected by the nature of the linker. Notably, modulation of the π-conjugated coumarin–phthalocyanine dyad CAPc and CSPc resulted in a large red-shift (Q-band above 710 nm); in particular, the dyad CAPc showed remarkably intense absorption in the spectral window of 450–650 nm. Electrochemical data for the dyes indicated that the azo double-bond-linked coumarin–phthalocyanine dyad dyes possessed relatively low-lying EHOMO values, which may be beneficial to suppress electron back-transfer from the conduction band of TiO2 to oxidized dyes due to facile regeneration of the oxidized dye by the electrolyte. Thermogravimetric analysis showed that the three coumarin–phthalocyanine dyad sensitizers were stable above 200 °C. When the dyads were applied as light-harvesting sensitizers in dye-sensitized solar cells, the cell sensitized by OAPc showed the best power conversion efficiency of 2.4%.