Structural modification for expanding near-infrared absorption and optimizing the optoelectronic properties of...

To investigate the influence of molecular structure on the optoelectronic properties of unsymmetrical squaraine dyes, this study conducted a systematic theoretical simulation analysis of two dye molecules, SD1 and SD3, and comprehensively evaluated their potential as photosensitizers in dye-sensitized solar cells (DSSCs). Meanwhile, using the SD3 molecule with superior optoelectronic properties as the parent molecule, we introduced conjugated π-bridges (-DTS and -DTT) and an anchoring group (cyanoacrylic acid (-CA)) to design four dye molecules (SD3-DTS, SD3-DTT, SD3-CA, and SD3-DTS-CA), and further investigated the mechanisms by which these two design strategies modulate the optoelectronic properties of the dyes. Both modification strategies effectively modulated the energy level structure, absorption spectra, electronic structure parameters, charge transport, and dye regeneration performance of the dye molecules. The light-harvesting efficiency (LHE) of all designed molecules was significantly enhanced, and SD3-CA and SD3-DTS-CA extended the light-harvesting ranges to the near-infrared region. Calculations indicate that SD3-DTS-CA exhibits excellent performance parameters, such as the smallest chemical hardness (h), electron reorganization energy (λ_e) and the largest LHE. Ultimately, SD3-DTS-CA demonstrated the optimal optoelectronic performance, including the short-circuit current density (J_SC) of 24.218 mA cm^-2, open-circuit voltage (V_OC) of 0.543 V and power conversion efficiency (PCE) of 10.712%, owing to the synergistic effect of -DTS and -CA. Furthermore, the PCEs of all designed molecules improved significantly compared with SD3, indicating that this modification strategy can reliably guide performance optimization of DSSC dye sensitizers.