investigation of the π-bridge role for imidazole derivative dyes in dye sensitized solar cell: theoretical study

a series of metal-free imidazole derivative dyes (c2, c3, c4, and c5) are virtually designed based on the original synthesized dye (e)-3-(5-(4,5-bis(4-(diphenylamino)phenyl)-1-ethyl-1himidazol- 2-yl)thiophen-2-yl)-2-cyanoacrylic acid (c1). all these dyes are designed by varying the π-bridge parts for dyesynthesized solar cells. the photovoltaic and optoelectronic properties have been investigated theoretically by using density functional theory (dft) and time-dependent density functional theory (td-dft) methods. many parameters have been investigated and evaluated to influence the modulation of the π- bridge groups. the optimization geometries, electronic structures, electronic absorption spectra, highest occupied molecular orbital (homo), lowest unoccupied molecular orbital (lumo), energy gap, and oscillator strength of all these dyes were characterized and investigated theoretically. from the results, the c2 dye (with two thiophene molecules as a spacer) was shown to have the lowest energy gap (1.91 ev) and the lowest lumo, which indicates that the dye has the best electron injection to the tio2 surface than other dyes.