Novel organic dyes based on thioindigo for dye-sensitized solar cells

•Two novel organic dyes based on thioindigo for DSSCs were synthesized.•Use of thioindoxyl, as the electron donor, as well as a stable light fast base.•Both dyes showed J-type aggregation on nano TiO2.•The dyes shows high PCE (η D1 = 6.10% and η D2 = 6.45%) in standard devices.

Two novel metal free organic dyes based on thioindigo were prepared and used as sensitizers in dye-sensitized solar cells. The synthesized dyes together with their corresponding intermediates were purified and characterized by analytical techniques. Such techniques confirmed the corresponding structures of dyes and their intermediates and the yield of all the stages of dye preparation were calculated to be above 75%. Fluorometric analyses show fluorescence in the red region of the visible spectrum for both dyes. Oxidation potential measurements for both dyes ensured an energetically permissible and thermodynamically favourable charge transfer throughout the continuous cycle of photo-electric conversion. Finally, dye sensitized solar cells were fabricated in order to determine the photovoltaic behaviour and conversion efficiencies of each dye. Such evaluations demonstrate rather high conversion efficiencies of 6.10% and 6.45% for such simple structured dyes 1 and 2, respectively.