Design and Theoretical Investigation of D–A′–π–A Sensitizers for Enhanced Dye‐Sensitized Solar Cells

Abstract Enhancing the performance of dye‐sensitized solar cells (DSSCs) requires strategic molecular engineering, particularly through the modulation of π‐spacer units to improve electron transport and device stability. In this study, three novel D–A′–π–A structured dyes (M1–M3) were systematically designed, incorporating coumarin as the donor (D), diketopyrrolopyrrole (DPP) as the auxiliary acceptor (A′), and cyanoacrylic acid as the main acceptor (A) fragments, with variations in the π‐spacer segment. The impact of these π‐spacers on the dye's optoelectronic and photovoltaic properties was thoroughly investigated in both isolated and solvent environments. Key performance metrics such as light‐harvesting efficiency (LHE), electron injection into the TiO 2 surface, absorption spectra, open‐circuit voltage, free injection energy (Δ G inject ), free regeneration energy (Δ G reg) , and energy gaps ( E gap ) were evaluated. Among the designed dyes, M2 and M3 exhibited narrower energy gaps of 1.91 and 1.61 eV, respectively, compared to the reference dye (1.94 eV), along with favorable negative Δ G inject values. M3 displayed a prominent redshift in absorption ( λ max = 740. nm), indicating its enhanced light absorption capability for solar applications, whereas M2 ( λ max = 603 nm) had a slightly lower value than the that of reference (604 nm). Furthermore, detailed analysis of frontier molecular orbitals (FMOs), molecular electrostatic potential (MEP) maps, transition density matrices (TDM), density of states (DOS), and natural bond orbitals (NBO) confirmed more efficient intramolecular charge transfer (ICT) in M3. These results underline the promising potential of the designed dyes, especially M3, as efficient sensitizers for next‐generation DSSCs.