Structure–Property Relationships in Triphenylamine-Based p-Type Organic Dyes for Dye-Sensitized Solar Cells: A Theoretical Study

The design of efficient organic sensitizers for dye-sensitized solar cells (DSSCs) depends critically on understanding their electronic structure and optical absorption behavior, as these properties directly influence light harvesting, charge separation, and electron injection efficiency. Triphenylamine-based p-type organic dyes are promising sensitizers owing to their strong electron-donating nature, molecular stability, and structural versatility. In this work, a systematic theoretical investigation is performed to elucidate the electronic and optical properties of a series of triphenylamine-derived organic dyes using density functional theory (DFT) and time-dependent density functional theory (TD-DFT).

Ground-state geometries are optimized at the B3LYP/6-31G* level to determine the highest occupied and lowest unoccupied molecular orbital (HOMO–LUMO) energies and their spatial distributions, which are crucial for effective charge transfer and energetic alignment in DSSCs. The analysis shows that structural modifications within the triphenylamine framework strongly affect orbital localization and energy gaps, thereby influencing intramolecular charge-transfer characteristics. TD-DFT calculations are employed to simulate optical absorption spectra, focusing on absorption intensity and spectral position in the visible region. The results demonstrate that extending π-conjugation and enhancing molecular planarity lead to red-shifted absorption bands with increased oscillator strengths, improving overlap with the solar spectrum and suggesting enhanced photocurrent generation.

Molecular electrostatic potential surface analysis further reveals the distribution of electron-rich and electron-deficient regions, providing insight into the role of functional groups in facilitating donor–acceptor interactions and charge redistribution. Overall, this study establishes clear structure–property–performance relationships and offers practical design guidelines for developing triphenylamine-based organic dyes with improved light-harvesting capability and potential DSSC efficiency.