First Principles Design of Dye Molecules with Ullazine Donor for Dye Sensitized Solar Cells

We design a series of metal-free donor-pi-bridge molecules (denoted VB0-VB4) based on a new donor group-ullazine donor-as sensitizers for dye sensitized solar cell (DSSC) applications. Density functional theory (DFT) and time-dependent DFT calculations reveal that the physical properties of dyes, including spectral response, light harvesting efficiency, and electron injection rate, are systematically improved by combining ullazine donor to a series of length changing pi bridges. Dye VB2 is the best candidate thanks to its outstanding performance on key parameters and achieving a balance between competing factors. Compared to two other series of molecules-L and M dyes, which differ from VB dyes by only the donor group-VB dyes have the largest light harvesting efficiency and the largest number of electrons injected to the conduction band of TiO2. These results suggest that the ullazine group can serve as an excellent donor for future DSSC applications.