Molecular Design of D--A-A Organic Dyes Based on Triphenylamine Derivatives with Various Auxiliary Acceptors for High Performance DSSCs

In this work, 11 newly designed organic dyes with D--A-A structure based on a 3D triphenylamine derivative known as indacenodithiophene-triphenylamine (IDTTPA) as a core, benzoic acid as the anchoring group and linked by various spacer fragments containing electron-acceptor character have been theoretically studied using density functional theory (DFT) and time-dependent DFT (TD-DFT) for dye-sensitized solar cells (DSSCs). This three-dimensional structure is very important in retarding dyes aggregation and charge recombination, besides enhancing the power conversion efficiency (PCE) of DSSC, we have further employed various auxiliary acceptors to facilitate the electron transfer from the donor to the acceptor. Seven different functionals containing 0-100% Hartree-Fock (HF) exchange and three solvent models have been tested in this study. Comparison between computational and experimental absorption of D1 indicates that the maximum wavelength was accurately reproduced by a BHandHLYP functional and solvation model based on density (SMD) solvent model. The molecular structures, energy levels, absorption spectra, light harvesting efficiency (LHE) and driving force of injection (G(inject)) are calculated. To sum up, these results indicate that the addition of an auxiliary acceptor into the core of the dye molecule has a significant effect on several properties including the planarity showed in this investigation, the decreasing in gap energy of 1.15eV, and a bathochromic shift of 180nm. It was found that the dye D4 with auxiliary acceptor 1,2,5-thiadiazolo[3,4-d]pyridazine shows a strong tendency to planarization, and possess the lowest values for bandgap of and open-circuit photovoltage 1.544eV and 0.733eV, respectively, the highest Ginject value (-1.23eV) and a maximum wavelength absorption of 608.85nm, which makes this dye exhibits positive results and can be used as a promising candidate for DSSCs.