Effect of Side Substituents Incorporated into π‐Bridges of Quinoxaline‐Based Sensitizers for Dye‐Sensitized Solar Cells

Abstract

Two new metal‐free donor (D)–acceptor (A)–π–A‐type sensitizers with 2,3‐dihexylquinoxaline (HQ) and 2,3‐diphenylquinoxaline (PQ) moieties as additional acceptors, respectively, coded as ZW002 and ZW003, are synthesized and applied in dye‐sensitized solar cells (DSSCs). Both dyes have broad absorption and large molar absorption coefficients. The sensitizer with the HQ core effectively restrains intermolecular aggregation due to steric hindrance of numerous alkyl chains. A thienyl unit with or without a hexyl branch is used as a π‐bridge. Incorporation of only thienyl groups as a π‐bridge into the sensitizer increases the dye‐loading amount on the TiO2 film due to the smaller molecular size. Using the ZW002 dye with the Co (II/III) redox couple results in DSSCs that exhibit a high photovoltaic conversion efficiency of 8.23% and short‐circuit current density (Jsc) of 12.43 mA cm−2, an open‐circuit voltage (Voc) of 960 mV, and a fill factor (FF) of 0.69. Although ZW003 shows a wider absorption range than that of ZW002, the two additional phenyl groups on the quinoxaline unit contribute to poorer performance (power conversion efficiency [PCE] of 7.43%) due to more serious dye aggregation.