New bithiazole-functionalized organic photosensitizers for dye-sensitized solar cells

Five bithiazole-based organic dyes D₁-D₅ containing different electron donor moieties (thiophene, uorene, carbazole, and triarylamine) in the molecular frameworks were synthesized, characterized and applied in dye-sensitized solar cells (DSSCs). The effects of electron-donating moieties of the organic dyes on their photophysical, electrochemical, and photovoltaic properties have been investigated in detail. These dyes exhibit strong charge transfer absorption bands in the visible region. Their redox potential levels were estimated by cyclic voltammetry and found to match well with the charge flow in DSSCs. The combination of broad absorption bands with fairly high extinction coefficients and appropriate redox properties makes these bithiazole-based molecules promising dyes for DSSCs. For solar cell device based on D₄, the maximal monochromatic incident photon-to-current conversion efficiency (IPCE) can reach up to 68.5%, with a short-circuit photocurrent density (J_sc) of 9.61 mA cm^-2, an open-circuit photovoltage (V_oc) of 0.70 V and a fill factor (FF) of 0.70, which results in a power conversion efficiency (PCE) of 4.65% under illumination of an AM 1.5 solar cell simulator.