Di(4-methylphenyl)methano-C60 Bis-Adduct for Efficient and Stable Organic Photovoltaics with Enhanced Open-Circuit Voltage

Abstract

A new class of fullerene bis-adducts—di(4-methylphenyl)methano-C60 bis-adduct (DMPCBA), di(4-fluorophenyl)methano-C60 bis-adduct (DFPCBA), and diphenylmethano-C60 bis-adduct (DPCBA)—were rationally designed and easily synthesized. Compared to the lowest unoccupied molecular orbital (LUMO) energy level of PC61BM (−3.95 eV), the double functionalization effectively raises the LUMO energy levels of these fullerene materials to ca. −3.85 eV, regardless of the substituent groups (CH3–, F–, and H−) at the para-position of the phenyl rings. This phenomenon suggests that the plane of the phenyl groups is preferentially parallel to the fullerene surface, leading to poor orbital interactions with C60 and negligible electronic effect. Importantly, such geometry sterically protects and shields the core C60 structure from severe intermolecular aggregation, rendering it intrinsically soluble, morphologically amorphous, and thermally stable. The device based on the P3HT:DMPCBA blend exhibited an open-circuit voltage (Vo...