Novel push-pull dyes with cyclic ring spacers (titanol, chromol, ferrol, nickelol, and zinkol): a DFT study for optoelectronic optimization in DSSCs.

Context: This computational investigation delves into the strategic design of bimetallic Zn/M organometallic D-π-A dyes for dye-sensitized solar cells (DSSCs), with a focus on how transition metals (Ti, Cr, Fe, Ni) modulate optoelectronic behavior and photovoltaic performance. Employing density functional theory (DFT) and time-dependent DFT (TD-DFT) simulations, four dyes (Dye1-Dye4) were systematically evaluated for their light-harvesting efficiency (LHE), charge transfer kinetics, and stability under vacuum and tetrahydrofuran (THF) solvation. The results underscore distinct metal-dependent trade-offs: the chromium-based dye (Dye2) demonstrates outstanding visible-light absorption (λ_max = 570 nm) with a high LHE (85%) and oscillator strength (f = 0.830), whereas the nickel-based dye (Dye4) exhibits redshifted absorption (λ_max = 609 nm) and an extended excited-state lifetime (τ = 1.55 ns), advantageous for charge separation. Titanium (Dye1) and iron (Dye3) variants emerge as economical alternatives, offering moderate efficiency and stability. THF solvation induces pronounced bathochromic shifts (+ 138 nm for Dye1) and thermodynamically favorable interactions (ΔG_solv <  - 61 kcal·mol⁻¹), enhancing light absorption and stability. Critical metrics such as electron injection energy (ΔG_inj), open-circuit voltage (V_oc), and regeneration energy (ΔG_reg) emphasize the need to harmonize optical performance with charge management. The study advocates co-sensitization of Dye2 and Dye4 to synergistically broaden spectral response and boost power conversion efficiency. These findings pave the way for sustainable DSSCs leveraging earth-abundant metals, aligning with global initiatives for green energy innovation.

Method: All calculations were performed with Gaussian 16. Ground state geometries were optimized by DFT with the B3LYP functional. The LanL2DZ basis set was used for transition metals, while 6-31 +  + G(d,p) was used for non-metallic atoms. The solvation models studied are the CPCM (Conductor Polarizable Continuum) model and the SMD (Solvation Model Density) model. Excited state properties have been calculated using TD-DFT with the CAM-B3LYP functional to evaluate electronic transitions.