Design of butterfly type organic dye sensitizers with double electron donors: The first principle study

In this work, we designed a series of butterfly type organic dyes, named ME07-ME13 by introducing such as triphenylamine, phenothiazine, coumarin groups etc. as electron donors and further investigated their absorption spectra using density functional theory (DFT) and time-dependent DFT (TDDFT). All designed dyes cover the entire visible absorption spectrum from 300 to 800nm. It's fascinating that ME13 molecule has two absorption peak and the molar coefficient of two absorption peaks are above 4.645×10⁴M^-1·cm^-1. The light absorption area of ME13 exhibits an increment of 16.5-19.1% compared to ME07-ME12. Furthermore, we performed a detailed analysis on their geometrical and electronic properties, including molecular structures, energy levels, light harvesting efficiency (LHE), driving force (ΔG_inject), regeneration (ΔG_regen),electron dipole moments (μ_normal), intermolecular electron transfer and dye/(TiO₂)₃₈ system electron transitions. The results of calculation reveal that double coumarin donors in ME13 are promising functional groups for butterfly type organic dye sensitizers. It is expected that the design of double donors can provide a new strategy and guidance for the investigation in high efficiency dye-sensitized devices.