Molecular engineering of D–D–π–A type organic dyes incorporating indoloquinoxaline and phenothiazine for highly efficient dye-sensitized solar cells

Abstract

Four metal-free organic dyes QX05–08 based on indoloquinoxaline and phenothiazine have been successfully designed and synthesized for dye-sensitized solar cells. The D–D–π–A type dyes QX07 and QX08 consist of an indoloquinoxaline donor, a phenothiazine donor, a cyanoacrylic acid acceptor/anchoring group and a thiophene or furan π-bridge. Other simple D–π–A type dyes QX05 and QX06 based on indoloquinoxaline and phenothiazine respectively have also been synthesized for comparison. The D–D–π–A type dyes QX07 and QX08 present good balanced structures and show excellent photoelectric properties. Especially, the dye QX07 with a thiophene unit as the π-bridge exhibits the best photovoltaic performances in solar cells. A high power conversion efficiency up to 8.28% with a Jsc of 15.3 mA cm−2 and a Voc of 757 mV have been achieved by the dye QX07 using an iodine electrolyte under standard conditions.