Design a New D-π-A Formation Dyes as Dye-sensitized Solar Cells Applications/ a DFT and TD-DFT Study

Dye-sensitized solar cells (DSSCs) have garnered significant interest among researchers in the field of photovoltaics due to their promising performance, low cost and easy process of fabrication. In this study, we have designed new D-π-A systems as derivatives of the reference (Ref. A) D-A-D scaffold, incorporating different π-bridges to enhance and optimize their efficiency as sensitizing dyes for DSSCs applications. Density functional theory (DFT) and time-dependent DFT (TD-DFT) methods were employed to investigate the geometrical and electronic structures, chemical reactivity indices, optical properties, exciton binding energy, and electrochemical properties of these dyes. We also examined the preferred adsorption process of the two selected dyes on a (TiO₂)₁₅ cluster model. The results demonstrate that all the dyes exhibit improved open-circuit photovoltage, enhanced light-harvesting efficiencies, higher electron injection efficiency, and excellent photovoltaic efficiency. Moreover, there is evidence of electron injection occurring from each studied dye to the conduction band of TiO₂, followed by efficient regeneration. The introduced bridges in the molecular systems play a crucial role in facilitating electron transfer from the donor to the acceptor region. Comparatively, the D-π-D systems exhibit superior performance in DSSCs compared to Ref. A, which can be attributed to their higher energy levels of the lowest unoccupied molecular orbital and larger oscillator strengths for the most excited states involving intramolecular electron transfer and the electron injection process occurring from each examined molecule to the conduction band of TiO₂, followed by subsequent regeneration. Overall, the results of our study highlight the potential of all the D-π-A systems as promising sensitizers for DSSCs applications, owing to their favorable optical and electronic properties and impressive photovoltaic parameters.