Dithienothiophene (DTT)-based dyes for dye-sensitized solar cells: synthesis of 2,6-Dibromo-DTT

A one-pot synthesis of 2,6-dibromodithieno[3,2-b;2′,3′-d]thiophene (dibromo-DTT, 4) was developed. A key step was bromodecarboxylation of DTT-2,6-dicarboxylic acid, obtained by saponification of the diester 1. The donor-acceptor dye DAHTDTT (13), based on a central 2,6-bis[2′-(3′-hexylthienyl)]dithieno[3,2-b;2′,3′-d]thiophene core (9), was prepared and incorporated in a dye-sensitized solar cell (DSC), which exhibited an energy conversion efficiency of 7.3% with Voc of 697 mV, Jsc of 14.4 mA/cm2, and ff of 0.73 at 1 sun.