Molecular Design of Efficient Organic D-A-π-A Dye Featuring Triphenylamine as Donor Fragment for Application in Dye-Sensitized Solar Cells.

A metal-free organic sensitizer, suitable for the application in dye-sensitized solar cells (DSSCs), has been designed, synthesized and characterized both experimentally and theoretically. The structure of the novel donor-acceptor--bridge-acceptor (D-A-pi-A) dye incorporates a triphenylamine (TPA) segment and 4-(benzo[c][1,2,5]thiadiazol-4-ylethynyl)benzoic acid (BTEBA). The triphenylamine unit is widely used as an electron donor for photosensitizers, owing to its nonplanar molecular configuration and excellent electron-donating capability, whereas 4-(benzo[c][1,2,5]thiadiazol-4-ylethynyl)benzoic acid is used as an electron acceptor unit. The influences of I-3(-)/I-, [Co(bpy)(3)](3+/2+) and [Cu(tmby)(2)](2+/+) (tmby=4,4,6,6-tetramethyl-2,2-bipyridine) as redox electrolytes on the DSSC device performance were also investigated. The maximal monochromatic incident photon-to-current conversion efficiency (IPCE) reached 81% and the solar light to electrical energy conversion efficiency of devices with [Cu(tmby)(2)](2+/+) reached 7.15%. The devices with [Co(bpy)(3)](3+/2+) and I-3(-)/I- electrolytes gave efficiencies of 5.22% and 6.14%, respectively. The lowest device performance with a [Co(bpy)(3)](3+/2+)-based electrolyte is attributed to increased charge recombination.