LAUSR

A set of D–A–π–A dyes containing a carbazole donor, linker composed of a naphthalimide auxiliary acceptor and spacers such as phenyl, oligothiophene, dithienopyrrole and cyanoacrylic acid acceptor have been synthesized and characterized. Influence of spacers on the optical and photovoltaic properties are analyzed. Nature of the spacer between naphthalimide and cyanoacrylic acid show significant effect on the absorption maximum. Elongation of conjugation and increment in electron richness gradually red shift the absorption. It also helps to tune the oxidation potential of the dyes. All dyes possess high-lying LUMO and low-lying HOMO when compared to CB of TiO2 and reduction potential of iodide electrolyte, which facilitate the electron injection into TiO2, and regeneration of the oxidized dye by electrolyte, respectively. A dye containing dithienopyrrole led to maximum photocurrent density of 3.60 mA cm−2 and an open circuit voltage of 519 mV in the series. This is attributed to the diminished resistance for charge transfer and long-lived electron lifetime when compared to the other dyes. The electrochemical impedance spectroscopy revealed small charge recombination resistance at TiO2/dye/electrolyte interface for all the dyes attesting the low open circuit voltages of the devices.