Exploring Different Designs in Thieno[3,4-b]pyrazine-Based Dyes to Enhance Divergent Optical Properties in Dye-Sensitized Solar Cells

Two novel organic sensitizers for Dye-Sensitized Solar Cells (DSSC), called TP1 and TP2, based on the electron-poor thieno[3,4-b]pyrazine (TPz) ?-bridge and the electron-rich N,N-bis(4-(hexylthio)phenyl)aniline (TPA) were designed following two different approaches: the classical D-A-?-A design and a symmetric structure with double anchoring functions. Both compounds were prepared exploiting short synthetic pathways based on direct arylation strategies and possibly one-pot desymmetrization. The two novel dyes displayed opposite optical properties: a broad and intense light absorption over the entire visible spectrum for TP1, and a localized absorption that peaked in the center of the visible region for TP2, resulting in a pitch-dark coloration and a green tone, respectively. When assembling the photovoltaic devices, different electrolyte compositions were explored to enhance the optical properties of the dyes. Power conversion efficiencies as high as 5.2% under full sun intensity were recorded for small test devices. The composition of the light transmitted through the TP2-containing transparent DSSC fits well with the human eye sensitivity spectrum, thus fulfilling the transparency requirements for building-integrated photovoltaics (BIPV).