Exploring the optoelectronic and photovoltaic properties of Ru-Arene complexes: DFT and TD-DFT insights into DSSC performance

Abstract

A series of seven half-sandwich organometallic Ru-arene complexes of the form $\left[\left({\eta }^6-p-\text{cymene}\right)\text{RuCl}\left({\text{LL}}^{\prime }\right)\right]P{F}_6^{-}$ were generated and analyzed using the Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT) approaches in both the gas phase and acetonitrile solution. These complexes were characterized by N,S-chelating ligands containing donating (-CH₃,-H, and –OH) and withdrawing (-Cl, -CF₃, -COOH, and –NO₂) groups, and the significance of these groups in determining the properties of the molecules was evaluated. The efficiency of dye-sensitized solar cell (DSSC) technology was also examined using various photovoltaic and optoelectronic indicators, including absorption spectra (λ_max, E_ex, OS), HOMO-LUMO gap, molecular orbital density, the efficiency of collecting light (LHE), electron injection's driving force (ΔG_inj), and regeneration's free energy (ΔG_reg). Our TD-DFT findings suggest that the dyes Ru3(-COOH) and Ru4(-NO₂) exhibit the largest absorption maxima and the highest LHE in the gas phase, owing to the presence of the stronger electron-withdrawing groups (-COOH and –NO₂). Furthermore, our observations indicate that stronger electron-withdrawing groups enhance the photovoltaic performance of DSSCs; decreased band gap, minimized electron recombination and quicker dye regeneration were identified as crucial factors in improving performance characteristics in the gas phase. However, in the acetonitrile phase, Ru7(-OH) demonstrated a significantly increased LHE, whereas Ru3(-COOH) experienced a notable decrease. Thus, we propose that Ru3(-COOH) and Ru4 (-NO₂) are more effective in converting sunlight into electricity compared to the other complexes studied in the phase gas, while Ru7(-OH) and Ru4(-NO₂) exhibit superior performance in the acetonitrile phase. These findings provide significant insight into the molecular design of metal complex sensitizers used in DSSCs highlighting the crucial role of ligand electronic effects and solvent interactions in optimizing photovoltaic performance.