Benzothiadiazole containing D-pi-A conjugated compounds for dye-sensitized solar cells: synthesis, properties, and photovoltaic performances.

Two D-pi-A conjugated molecules, BzTCA and BzTMCA, were developed through facile synthetic approaches for dye-sensitized solar cells. The investigation of the photophysical properties of BzTCA and BzTMCA both in dilute solutions and in thin films indicates that their absorption exhibits a wide coverage of the solar spectrum. The absorption features for BzTCA and BzTMCA commence at about 710 nm in solution, and at about 800 nm in the solid state. The absorption maxima (lambda(max)) for both BzTCA and BzTMCA on TiO(2) film are almost the same as those in dilute solution. Their HOMOs and LUMOs were found to partly overlap at the center of these dyes, which guarantees appreciable interactions between the donors and acceptors. The investigation of the performance of dye-sensitized solar cells fabricated from BzTCA and BzTMCA indicated that the power-conversion efficiencies are 6.04 % and 4.68 %, respectively, which could be comparable with the normal sensitizer N3. BzTMCA showed lower incident photon-to-electron conversion efficiency (IPCE) and J(sc) values relative to BzTCA, which is probably because of the weaker driving force of dye regeneration and electron injection process of BzTMCA. The IPCE responsive area reached nearly 800 nm, which provides great potential for further improvement of the photocurrent density and power-conversion efficiency. Our investigations demonstrate that both dyes BzTCA and BzTMCA could be promising candidates for dye-sensitized solar cells.