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-πA-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 (JSC) was calculated by considering the free energy of charge injection (ΔGinject), the free energy of dye regeneration (ΔGreg), 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 JSC, hence affecting the overall photoelectric conversion efficiency. Dye 9 demonstrated better electron transfer performance, with qCT (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 훽tot 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.