Design of a D-π-A-A framework with various auxiliary acceptors on optoelectronic and charge transfer properties for efficient dyes in DSSCs: A DFT/TD-DFT study

Derived from an excellent light harvester, an iminodibenzyl-substituted porphyrin sensitizer consisting of a series of D-nA-A structural motifs, was investigated using density functional theory (DFT) and time-dependent DFT methods to demonstrate the effects of various auxiliary acceptors on sensitizers. Absorption spectra simulations at 417.51 nm calculated using CAM-B3LYP with a mixed LanL2DZ/6-31G(d,p) basis set exhibited good agreement with the experimental results (i.e., 426.60 nm). Impressively, the introduction of a co-acceptor moiety on the sensitizers effectively shifted the light absorption to the NIR region. The computational results showed that Dye 9 notably exhibited the smallest HOMO-LUMO energy gap (3.34 eV). The Q band of Dye 9 was located at 756.72 nm, which was the largest wavelength and the most redshifted absorption spectrum. The short-circuit current density (J(SC)) was calculated by considering the free energy of charge injection (Delta G(inject)), the free energy of dye regeneration (Delta G(reg)), and light-harvesting efficiency (LHE). The oscillator strength of the maximum absorption was greatest for Dyes 3 and Dye 9, resulting in increase LHE and improved J(SC), hence affecting the overall photoelectric conversion efficiency. Dye 9 demonstrated better electron transfer performance, with q(CT) (0.630 e(-)), which was attributed to its better planarity compared to other dyes. Interestingly, Dye 9 exhibited substantially enhanced nonlinear optical response through intramolecular charge transfer process, with a beta(tot) value many-fold higher than that of urea computed at the same theoretical level. It indicates that the studied dye molecules are potential candidates for the optoelectronic applications. Dye 9 was therefore the most feasible dye candidate for efficient DSSC applications. [GRAPHICS] .

Automated summary

The effects of auxiliary acceptors on sensitizers were investigated, and the most feasible dye candidate for efficient DSSC applications, Dye 9, was identified, based on the comparison between computational simulations and experimental results of absorption spectra and photoelectric conversion efficiency.