A study on indolo[3,2,1-]carbazole donor-based dye-sensitized solar cells and effects from addition of auxiliary donors.

Density functional theory has been employed to study indolo[3,2,1-]carbazole donor-based dyes, incorporating one and two units of 2,4-dimethoxybenzene auxiliary donors. Electrostatic potential analysis highlights the dye with one auxiliary donor (D2) as having the highest charge-donating capability. Structural analysis shows that auxiliary donors enhance planarity, reduce steric hindrance, and improve π-conjugation. Highest occupied molecular orbital (-6.025 to -5.660 eV) and lowest unoccupied molecular orbital (-2.927 to -2.844 eV) of all dyes support efficient electron injection into the semiconductor and dye regeneration process. Auxiliary donors enhance chemical reactivity parameters, improving the suitability of these dyes for dye-sensitized solar cells (DSSCs). Inclusion of extra donors reduces the excitonic binding energy, minimizing recombination losses, and increases polarization, enhancing the charge injection efficiency. Additional analyses explored properties such as charge separation, charge transfer length, transition density matrix and non-covalent interactions. All dyes exhibit strong absorption (410-440 nm) in the visible region, confirming their applicability to DSSCs, while emission spectra provide insights into their fluorescence lifetimes. D2 demonstrates improved performance in specific properties. However, D3, with two auxiliary donors, achieves the best overall balance across other computed parameters. Indeed, the inclusion of auxiliary donors induces significant changes and may be considered as a valuable strategy for designing efficient DSSCs.