Quantum Chemical Modeling Approach Toward Phenothiazine‐Based DyeSensitized Solar Cells: Role of Tetracene and Pentacene π ‐Spacers in Photovoltaic and Electrochemical Performance

Four phenothiazine‐based organic dyes (PTZ3‐PTZ6) have been modeled by systematically varying the π ‐spacer in the donor‐ π ‐acceptor (D‐ π ‐A) framework to enhance dye‐sensitized solar cells (DSSC) performance. Density functional theory (DFT) and time‐dependent DFT were employed to study electronic structures, charge transfer behavior, absorption spectrum, transition density matrix, noncovalent interaction, and photovoltaic characteristics to predict suitable DSSC candidates. The calculated negative Gibbs free energy for electron injection suggests the efficient charge transfer to the TiO 2 conduction band. Computed results also show that the dye PTZ6 predicted as the highest light‐harvesting efficiency (LHE) (82%), power conversion efficiency (1.988%), and a short‐circuit current density (2.23 mA cm −2 ) among all the studied dyes. An inverse correlation between LHE and chemical hardness is also observed which suggests that the PTZ6 dye incorporating pentacene as a π ‐spacer can hold a significant potential as a high‐performance sensitizer in DSSCs. These findings predict that π ‐spacer tuning between the donor and acceptor moieties effectively reduced the energy band gap and facilitated enhanced intramolecular charge transfer, and could be an effective strategy to optimize dye performance in DSSCs.