In silico evaluation of chromene-based D-π-A dyes for high-performance dye-sensitised solar cells
Kamakshi Sharma1, N B Singh1, Mridula Guin2
1Department of Chemistry and Biochemistry, Sharda University, Greater Noida, India.
Context:
This study provides an extensive computational investigation of six chromene-based dyes with customised donor and π-bridge structures designed for dye-sensitised solar cell (DSSC) applications. Using density functional theory (DFT) and time-dependent density functional theory (TD-DFT), we examine their energy levels, optical absorption characteristics, electronic density of states, transition density matrices, spin-density distributions, natural bond orbital (NBO) features, hydrophobicity, and reorganisation energies. The six dyes (M1-M6) display LUMO levels well above the TiO₂ conduction band (- 3.44 to - 3.73 eV) and HOMO levels below the I₃⁻/I⁻ redox potential (- 5.48 to - 5.69 eV), supporting favourable electron injection and dye regeneration. Among the series, M2 and M5 exhibit the narrowest HOMO-LUMO gaps (1.84 and 1.79 eV), indicative of enhanced intramolecular charge-transfer character and bathochromic shifts that improve light-harvesting capability. Notably, M5 possesses the lowest total reorganisation energy (0.281 eV), suggesting minimal geometric relaxation during charge redistribution. Together, these findings demonstrate how rational donor/π-linker modification enables fine-tuning of optoelectronic behaviour in chromene-based dyes and provides valuable design guidelines for developing efficient, metal-free, and low-cost DSSC sensitizers.
Methods:
All electronic structure calculations were performed using Gaussian 16, and molecular visualizations were generated with GaussView 6.0 program package. Geometry optimizations were carried out at the B3LYP/6-31G(d,p) level, while optical properties were computed using TD-CAM-B3LYP/6-31G(d,p) based on optimized ground-state geometries. Solvent effects were included using the CPCM model with dichloromethane as the solvent. GaussSum software was employed to analyze partial density of states (DOS) and Multiwfn software was used for transition density matrix (TDM) analysis. The reorganization energy of hole (λh) and electron (λe) was determined using the four-point Marcus approach.
