Theoretical Evaluation of Electron Transport in Aniline Tetramer-based Dye-sensitized Solar Cells

The essential electron transporting function of EPAT in phenyl-capped aniline tetramer (EPAT)/tert-butylpyridine (TBP)-based dye-sensitized solar cells (DSC) is evaluated by density functional theory (DFT). DFT-based molecular modeling coupled with molecular mechanics optimization reveal that EPAT molecules in-situ self-organizes to dimeric molecular complexes through van der Waals and Coulombic interactions. TBP molecules assist to form TBP-hydrogen-bonded EPAT complexes, (EPAT-H-TBP)2 and (EPAT-H-2TBP)2. The molecular complexes have stacked structures as well, and the electron-accepted states of radical anions, (EPAT-H-TBP)2.− and (EPAT-H-2TBP)2.− give narrow band gaps (0.26∼0.28 eV), and the singly occupied molecular orbitals (SOMO) are comparable in configurations with the lowest unoccupied molecular orbital (LUMO). We understand that electron in photo-irradiated EPAT/TBP phase should transport effectively by hopping on SOMO of (EPAT-H-TBP)2.− and (EPAT-H-2TBP)2.−.