D-A-π-A System: Light Harvesting, Charge Transfer, and Molecular Designing

Three organic dyes (XY1, XY2, and XY3), synthesized by inserting a thiophene heterocycle and shifting the position of benzothiadiazole (BTZ) auxiliary acceptor on the cyclopentadithiophene-(CPDT) pi-bridge, are theoretically investigated using density functional theory (DFT) and time-dependent DFT (TD-DFT) for their potential applications in solar cells. The photoelectric paremeters (short-circuit current, open circuit voltage, conversion efficiency) are evaluated by the following factors: energy levels and the orbital compositions, the absorption spectra, NBO analysis from S-0 to S-1, the qualitative descriptions of D-CD, Delta(r), S, and Delta Q for intramolecular charge transfer (ICT) processing, the adsorption energy (E-ads), and the excited lifetime (t), the shift of CB and vertical dipole moment (mu(normal)), the electron injection lifetime (tau), the Marcus rate of inner-path recombination, the simulation of outer-path recombination dye...I-2 and dye regeneration [dye(+center dot)I(-)], etc. The E-ads, the excited lifetime (t) and the electron injection lifetime (tau) explain., the order of experimental J(SC) and the trend of V-oc is interpreted by the calcuations on the Delta E-CB, mu(normal) the Marcus rate and the dye...I-2, mode. Among three molecules, XY2 possesses the significance advantage in ICT Mechanism and dye regeneration ability based on analysis of qualitative descriptions and two-step regeneration mechanism. Moreover, 12 dyes are designed by the substitution of pi-bridge of XY2, which provide a strategy to improve the abilities of absorption and electron injection as well as photoelectric properties on the-comparison of XY2.