Applications Of Quinoxaline-based Sensitizers In Dye-Sensitized Solar Cells

In order to synthesize more rigid photosensitizers,three dyes with different quinoxaline groups as π bridge were designed and synthesized in the subject.The optical properties,electrochemical properties,and the influence factors of different photovoltaic performance of dye–sensitized solar cell(DSSCs)of these dyes were studied.Two new metal–free D–A–π–A type sensitizers with 2,3–dihexylquinoxaline(HQ)and 2,3–diphenylquinoxaline(PQ)moieties as π bridge,respectively coded as ZW002 and ZW003,has been synthesized for application 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 π–π stacking owing 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 Ti O2 film owing to the smaller molecular size.Using the ZW002 dye with the[Co(bpy)3]2+/3+ redox couple results in DSSCs that exhibits a high photovoltaic conversion efficiency of 8.23% and short–circuit current density(Jsc)of 12.43 m A cm-2,an open–circuit voltage(Voc)of 960 m V and a fill factor(FF)of 0.69.Although ZW003 shows a wider absorption range than that of ZW002,the two additional phenyl groups grafted on the quinoxaline unit contributes to poorer performance(PCE of 7.43%)due to more serious dye aggregation.The D–A–π–A photosensitizer with a 2,3–dihexyl–6,7–bis(hexyloxy)quinoxaline group as a π bridge were synthesized and applied in DSSCs,named ZW001.The maximum absorption wavelength of the ZW001 dye is small and the absorption spectrum is narrow,which limits the photoelectric performance of the solar cell.In order to improve the performance of the DSSCs,the photosensitizers ZW001 and ZW003 were mixed at a concentration ratio of 3: 4 to form a dye bath,and the Ti O2 film was immersed in the dye bath for co–sensitization.The solar cells were assembled by using the cobalt electrolyte and the iodine electrolyte as the liquid electrolyte,respectively.When the electrolyte is [Co(bpy)3]2+/3+,After the co–sensitization,the UV–vis spectrum is broadened and the defect is compensated.Thus,the photovoltaic efficiency of ZW001 + ZW003(Jsc = 11.89 m A cm-2,Voc = 891 m V,FF = 0.72,PCE = 7.62%)is higher than the two single dyes.When the electrolyte is I–/I3–,the absorption spectrum also is broadened,but the efficiency of ZW001 + ZW003(6.20%)is higher than ZW001(5.40%)and lower than ZW003(6.94%).The dye–loading amount of ZW003 increases due to the five layers be printed on Ti O2 films.At the same dye concentration,the efficiency of all solar cells based on cobalt electrolyte is higher than that on iodine electrolyte,especially the difference in photovoltage.The I–/I3– electrolyte absorbs the sun light,and the energy losses due to the two steps of the regeneration mechanism.