Rational design of ruthenium-based organic sensitizers for high-performance dye-sensitized solar cells: a comprehensive DFT and TD-DFT investigation.

CONTEXT: In this work, we report a detailed computational evaluation of eight organic ruthenium-based sensitizers (Dye1-Dye8) for their possible use in Dye-Sensitized Solar Cells (DSSCs). The calculated electronic and photovoltaic parameters showed a good energetic alignment for electron injections and dye regeneration, with HOMO energies from -5.483 to -4.994 eV, LUMO energies from -3.271 to -2.933 eV and open-circuit voltage values from 0.694 to 1.183 eV. The quantum chemical descriptors showed excellent electronic reactivity with global hardness values from 1.002 to 1.239 eV and softness values between 0.403 and 0.499 eV-1, indicating a high charge transfer ability and electronic flexibility. Charge distribution analyses such as MEP and ELF showed strong donor-acceptor behavior and effective electron delocalization along the molecular framework. Structural investigations by RDG, NCI, and Hirshfeld surfaces revealed that hydrogen bonding and weak intermolecular contacts considerably increase molecular stiffness, crystal packing, and intermolecular electrical communication, with H···H interactions contributing 77-80% in Dye1, Dye2, and Dye7. Further DOS/PDOS research demonstrated a substantial orbital hybridization between Ru d-orbitals and ligand orbitals, confirming effective photoinduced excitation pathways. The optical characteristics exhibited extensive absorption in the visible and near-infrared areas with λmax values in the range of 436.891-788.532 nm, excitation energies from 1.573 to 1.721 eV, and oscillator strengths from 0.684 to 2.038, showing good light-harvesting performance. The obtained results highlight the extraordinary stability of structure, excellent electrical characteristics, and outstanding photovoltaic potential of the studied sensitizers for the development of future high-efficient DSSC devices.

METHODS

All calculations were done with DFT and TD-DFT in Gaussian and molecular visualization in GaussView. ωB97X-D functional with LanL2DZ basis set for Ru and Ti atoms and 6-31G(d,p) for the non-metal atoms were used for geometry optimizations. Frequency calculations verified genuine minima with no imaginary frequencies. The excited-state and optical properties were calculated at the CAM-B3LYP level of theory using TD-DFT for the first 30 singlet-singlet transitions. Other analyses are MEP, ELF, RDG, NCI, Hirshfeld surface, and DOS/PDOS calculations.