Push–pull triphenylamine based chromophores as photosensitizers and electron donors for molecular solar cells

A series of push–pull chromophores (1–6) comprising triphenylamine as donor and methylenethiazole, bearing electron-withdrawing groups in the 2′ position, as terminal acceptor groups have been developed. The resulting dyes were characterized by UV–vis and fluorescence spectroscopies, cyclic and OSWV voltammetries and thermal analysis. The low energy absorption band of these oligomers was located at 583–705 nm in solution. A significant positive solvatochromism, with excellent correlation with the Kamlet–Taft constant, was found confirming the charge transfer character of this band. Theoretical studies reveal a partial quinoid character in these compounds and a reduced band gap HOMO–LUMO energies of 1–6 derived from electrochemical and optical measurements were found to be suitable for their use as donor materials in combination with PCBM as acceptor in planar heterojunction solar cells. The studied devices, based on stacked cells connected electrically, incorporating these low band gap chromophores exhibited reasonable conversion efficiencies of up to 0.91% under air mass (AM) 1.5G illumination.