Naphthyl and thienyl units as bridges for metal-free dye-sensitized solar cells

A series of new organic dyes, comprising a naphthyl moiety as a π-conjugated bridge, different amines as donors, and a cyanoacrylic acid group as an electron acceptor and anchoring group, have been designed and synthesized for applications in dye-sensitized solar cells (DSSCs). One of the compounds was also characterized by single-crystal X-ray structural analysis. All of the dyes exhibited maximum absorptions in the range of 371-441 nm. The short-circuit photocurrent density, open-circuit voltage, and fill factor (FF) values of the devices are in the range of 6.13-10.90 mA cm ^-2, 0.62-0.69 V, and 0.62-0.67, respectively, corresponding to an overall conversion efficiency of 2.76-4.55 %. The conversion efficiency reached 38-62 % of that of a N719-based device (7.31 %) fabricated and measured under similar conditions. Steric congestion between the naphthyl and aromatic moieties jeopardizes charge transfer from the donor to the acceptor. Insertion of an alkenyl entity between the naphthyl entity and the aromatic ring alleviates steric congestion and leads to longer wavelength electronic absorption spectra.