High Molar Extinction Coefficient Branchlike Organic Dyes Containing Di(p-tolyl)phenylamine Donor for Dye-Sensitized Solar Cells Applications

Two novel branchlike organic dyes ( D1 and D2 ) comprising two di( p -toyl)phenylamine moieties as the electron donor, cyanoacetic acid moieties as the electron acceptor, thiophene or 3-hexylthiophene moieties as the Π-spacer, were designed and synthesized for dye-sensitized solar cells (DSSCs). It was found that the introduction of two di( p -tolyl)phenylamine groups to form the branchlike configuration exhibited better photovoltaic performance due to the improvement of the electron donating and the light-harvesting properties. By the introduction of two di( p -tolyl)phenylamine groups into the framework of D2, it is interesting to note that the UV−vis absorption of D2 showed an obvious blue-shift but also improved molar extinction coefficient compared with that of D3 . The transient absorption measurements showed that the dyes D1 and D2 with two di( p -tolyl)phenylamine-substitutes could effectively retard charge recombination between electrons at the TiO 2 and the oxidized dyes. Among the three dyes studied, a maximum power conversion efficiency of 6.41% was obtained under simulated AM 1.5 G solar irradiation (100 mW/cm 2 ) with a DSSC based on D2 dye ( J sc = 11.62 mA/cm 2, V oc = 0.73 V, FF = 0.756) upon the addition of 1.0 × 10 −3 M chenodeoxycholic acid (CDCA) as coadsorbent.