Novel metal-free organic dyes containing linear planar 11,12-dihydroindolo[2,3-a]carbazole donor for dye-sensitized solar cells: Effects of π spacer and alkyl chain

Abstract

Three novel D−π−A type dyes DC1∼3, which consisting of indolo[2,3-a]carbazole as donor scaffold linked to the acceptor/anchoring unit cyanoacetic acid via different π-spacers, were successfully designed and synthesized. The structure, photophysical and electrochemical properties, and photovoltaic properties of the three sensitizers were investigated in detail. The results indicate that the donor 11,12-bis(2-ethylhexyl)-11,12-dihydroindolo[2,3-a]carbazole with two branched alkyl chains is effective in inhibiting the intermolecular π−π aggregation effects, and the auxiliary alkyl chains in the π-bridge cause the DC3-based DSSCs to exhibit higher open circuit voltages than that of the devices based on dye DC2. Among all of the devices fabricated with the dyes, the DC3-based cells without chenodeoxycholic acid (CDCA) exhibit the best photovoltaic performance, with a short-circuit current density of 10.98 mA cm−2, an open circuit voltage of 752 mV and a fill factor of 0.725, corresponding to a highest power conversion efficiency of 5.98% in liquid electrolyte.