Tuning the optical and charge transfer properties of tetrathiafulvalene-based D–A′–π–A dyes for DSSCs: a DFT and TD-DFT investigation

This study has explored a series of new tetrathiafulvalene-based dyes designed using the D-A'-π-A framework for dye-sensitized solar cells (DSSCs). Twelve dyes have been developed by incorporating benzannulated heterocyclic auxiliary acceptors - 2,1,3-benzothiadiazole, 2<i>H</i>-benzotriazole, and 2-methylbenzotriazole - paired with four different π-spacers. Their structural, electronic, optical, and charge transfer properties have been analyzed using DFT and TD-DFT. The literature has suggested that integrating an auxiliary acceptor in D-A'-π-A architectures enhances band energy tuning and extends light absorption. This study has utilized tetrathiafulvalene within this framework alongside benzannulated heterocyclic auxiliary acceptors, demonstrating its effectiveness in optimizing key DSSC parameters. All designed dyes have exhibited well-aligned energy levels, favorable charge transfer characteristics, and strong light-harvesting capabilities, making them promising candidates for DSSC applications. Among them, B1 has emerged as the best performer, with a high charge transfer rate (14.8 × 10¹³ s^-1), a low reorganization energy (0.509 eV), and a strong light-harvesting capacity (0.93). These findings have underscored the potential of tetrathiafulvalene-based dyes with benzannulated heterocycles in DSSCs and have provided valuable insights for designing efficient organic solar materials.