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 TiO₂ 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/cm²) with a DSSC based on D2 dye (J_sc = 11.62 mA/cm², V_oc = 0.73 V, FF = 0.756) upon the addition of 1.0 × 10^-3 M chenodeoxycholic acid (CDCA) as coadsorbent.