Design and Synthesis of Near-infrared-active Heptamethine–Cyanine Dyes to Suppress Aggregation in a Dye-sensitized Porous Zinc Oxide Solar Cell

New heptamethine–cyanine dyes were synthesized and used for dye-sensitization of porous zinc oxide cells in the near-infrared region (800 nm). The introduction of alkyl groups into the cyclohexene and indolenium moieties remarkably prevented H-aggregation of the dyes. Consequently, the photovoltaic performance of the dye-sensitized zinc oxide cells with DCA was improved; a solar-to-electricity conversion efficiency (η) of 0.67%, a short-circuit current density of 2.22 mA cm−2, an open-circuit photovoltage of 0.46 V, and a fill factor of 0.66 under standard AM 1.5 irradiation (100 mW cm−2).