Di(4-methylphenyl)methano-C_(60) Bis-Adduct for Efficient and Stable Organic Photovoltaics with Enhanced Open-Circuit Voltage

摘要

A new class of fullerene bis-adducts—di(4-methyl-phenyl)methano-C_(60) bis-adduct (DMPCBA), di(4-fluorophe-nyfJmethano-C_(60) bis-adduct (DFPCBA), and diphenylmetha-no-C_(60) bis-adduct (DPCBA)—were rationally designed and easily synthesized. Compared to the lowest unoccupied molecular orbital (LUMO) energy level of PC_(61)BM (-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 C_(60) and negligible electronic effect. Importantly, such geometry sterically protects and shields the core C_(+60) 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 (V_(oc)) of 0.87 V, a short-circuit current density (J_(sc)) of 9.05 mA/cm , and a fill factor (FF) of 65.5%, leading to a high power conversion efficiency (PCE) of 5.2%, which is superior to that of the P3HT:PC_(61)BM-based device. Most significandy, the amorphous nature of DMPCBA effectively suppresses the thermal-driven aggregation and thus stabilizes the morphology of the P3HT:DMPCBA blend. Consequently, the device retained 80% of its original PCE value against thermal heating at 160 °C over 20 h.