Benzodithiophene and tetrathienylethene systems as efficient spacers in push-pull, metal-free DSSC sensitizers

Metal-based photosensitizers have been used over the last 20 years as the key components for Dye Sensitized Solar Cells (DSSC).[1] Although they exhibit high perforormances, they often require challenging synthesis and tricky purification steps. For these reasons, the development of metal-free, stable organic dyes with optical absorptions extending into red and near-IR region of the solar spectrum is, at present, a “hot topic” of the chemistry research in this field. In this frame, we have synthesized a series of novel metal-free dyes based on benzo[1,2-b:4,3-b’]dithiophene, (BDT), benzo[1,2-b:4,5-b’]dithiophene, (BDT1) and tetrakis(2-thienyl)ethene (TTE), concurrently testing various donor and acceptor terminal building blocks and linkers. The new chromophore series have been the object of a detailed molecular electrochemistry study, focusing on the electron transfer properties of the electron rich and electron poor terminal redox sites as a function of the conjugation efficiency of the linkerspacer system, of the substituent effects, and also, possibly, of double bond stereoisomerism. The electrochemical results are compared with spectroscopic and computational data, plus preliminary tests of the most promising systems as dyes. Figure 1.