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.