Theoretical design and characterization of high-efficiency organic dyes with different electron-withdrawing groups based on C275 toward dye-sensitized solar cells
Seven dyes 1–7 with different electron-withdrawing groups were designed and investigated based on C275, which has been the most efficient metal-free donor/acceptor dye until now to screen outstanding dyes for an organic dye-sensitized solar cell (DSSC). Some basic parameters, such as geometries, electronic structures, absorption spectra and charge recombination, were investigated by DFT and TDDFT methods, and the theoretical maximum short-circuit current density (Jmaxsc) and the electron injection lifetime (τ) were also calculated to estimate the light-harvesting abilities and electron injection efficiencies of these dyes, respectively, which adds some quantitative information for our study. Moreover, the charge recombination process was also discussed according to the distance (r) between the semiconductor surface and cation holes in the dye. The results show that all the dyes in our work exhibit ultrafast and effective electron injection with τ values in fs. Dyes 3, 5 and 7 have better light-harvesting abilities and dyes 1, 4 and 7 have better electron-collecting abilities with slower charge recombination than C275. Thus, the designed dye 7 might have superior performance in comparison with C275 and could be the most promising candidate as an organic dye in DSSCs.