Design and Computational Investigation of Multi‐Donor Ferrocene‐Based Dyes for DSSC: A DFT and TD‐DFT Study for Optoelectronic Optimization

This theoretical study investigates a series of linear push–pull ferrocene‐based dyes (D0–D5), featuring a D–D′–π–A–D″–A′ architecture, designed for dye‐sensitized solar cells (DSSCs). Density functional theory (DFT) and time‐dependent DFT (TD‐DFT) calculations were used to systematically assess the influence of various electron‐rich heterocyclic terminal donor groups (D″). A clear structure–property relationship is demonstrated: tuning the D″ group precisely modulates the absorption profile, leading to a progressive bathochromic shift that extends light harvesting into the near‐infrared region for dyes D4 and D5. Electron density, molecular electrostatic potential (MESP), and natural bond orbital (NBO) analyses confirm that the redshift is associated with enhanced intramolecular charge transfer and effective charge separation between the ferrocene donor and the acceptor. All dyes exhibit thermodynamically favorable electron injection (Δ G inj < 0) and feasible dye regeneration (Δ G reg ) energies. Although D5 shows the most red‐shifted absorption and the highest light‐harvesting efficiency (LHE = 0.97), dyes D2 and D3 emerge as the most promising candidates, offering the best compromise between theoretical open‐circuit voltage ( V oc ), excited‐state lifetime ( τ ), and fill factor (FF). This work provides a strong theoretical foundation, illustrating that strategic donor modification is a powerful tool for spectral tuning and guiding the design of high‐performance ferrocene‐based sensitizers.