Selective Fluorination on an Acridine-Based Self-Assembled Molecule for Optimal Interfacial Modification in Organic...

Self-assembled monolayers (SAMs) offer a powerful molecular-level approach to tuning the interface between indium tin oxide (ITO) anode and active layer in organic solar cells (OSCs). To realize better interfacial modification, herein, site-specific fluorinations of a kind of SAM material with 9,10-dihydro-9,9-diphenylacridine as the conjugated head are performed. Two fluorinated derivatives and their nonfluorinated parent compound, named 4PA-FPhAc, 4PA-PhAcF, and 4PA-PhAc, are synthesized. It is found that 4PA-FPhAc, containing fluorine atoms at the para-positions of the phenyl side chains on the acridine ring, exhibits stronger binding with ITO, enhanced intermolecular interactions, and a tendency to form a denser and more homogeneous molecular assembly, leading to improved interfacial energetic alignment and more efficient hole extraction. In contrast, fluorinations on the acridine backbone perturb molecular packing of 4PA-PhAcF and deteriorate interfacial contact. As a result, binary OSCs incorporating 4PA-FPhAc deliver an impressive efficiency of 19.56%, outperforming counterparts adopting 4PA-PhAc (18.78%) and 4PA-PhAcF (11.90%). Notably, 20.25 cm2 photovoltaic modules with the SAM of 4PA-FPhAc provide a high efficiency of 16.97%. This work demonstrates that site-selective fluorination is an effective molecular-tailoring strategy for high-quality SAMs applicable in OSCs.