Terminal Acceptor-Driven designing of fused Triphenylamine-Based organic small molecules with Bis-Dimethylfluorenyl peripheral moieties for advanced photovoltaics

Abstract

Organic electronic materials are a highly anticipated research area due to their potential in optoelectronic and photovoltaic applications. This study presents the rational design of small organic molecules for perovskite and organic solar cells. The design employs fused triphenylamine cores with peripheral bis-dimethylfluorenyl donor moieties and utilizes an end-capping acceptor design strategy with thiophene-based π-linkers. Five molecules (FA1-FA5) were designed, and their structural, electrochemical, photophysical, charge transport, and chemical stability properties were simulated using advanced quantum mechanical methods to establish structure–property relationships. Cyano-, fluoro-, methoxy-, and carbonyl-based electron-withdrawing terminal groups were incorporated to modulate the frontier orbital energy levels via the push–pull effect, achieving controlled stabilization of the HOMO and LUMO levels in the designed molecules. The calculated energy level alignments with perovskite layer suggest these molecules as promising hole transport materials for perovskite solar cells, potentially leading to enhanced open-circuit voltage. Furthermore, the near-degenerate HOMO energy levels with HOMO-1 and HOMO-2 are expected to promote charge transfer states and facilitate exciton dissociation efficiency. Notably, molecules FA2 and FA3 exhibit panchromatic absorption profiles spanning the Vis-IR region with high light harvesting potential, which is crucial for achieving high photocurrent generation in organic photovoltaics. The designed molecules possess high dipole moments and favorable negative solvation energies (−15.82 to −25.10 kcal/mol) in chlorobenzene for solubility, indicating good film-forming properties for device fabrication. Compared to the reference molecule DMFA-FAR, acceptor functionalization significantly reduces hole reorganization energy (0.112–0.135 eV), implying a corresponding increase in hole mobility. This, along with the strong intramolecular charge transfer and low exciton binding energy (0.08–0.21 eV), suggests efficient charge separation and reduced recombination losses in devices. Overall, this study demonstrates the effectiveness of the designed molecules as potential donors or hole transport materials for developing high-performance advanced photovoltaics.