Bispentafluorophenyl-Containing Additive: Enhancing Efficiency and Morphological Stability of Polymer Solar Cells via Hand-Grabbing-Like Supramolecular Pentafluorophenyl–Fullerene Interactions

Abstract

A new class of additive materials bis(pentafluorophenyl) diesters (BFEs) where the two pentafluorophenyl (C 6 F 5 ) moieties are attached at the both ends of a linear aliphatic chain with tunable tether lengths ( BF5, BF7, and BF13 ) were designed and synthesized. In the presence of BF7 to restrict the migration of fullerene by hand-grabbing-like supramolecular interactions induced between the C 6 F 5 groups and the surface of fullerene, the P3HT:PC 61 BM: BF7 device showed stable device characteristics after thermal heating at 150 °C for 25 h. The morphologies of the active layers were systematically investigated by optical microscopy, grazing-incidence small-angle X-ray scattering (GISAXS), and atomic force microscopy. The tether length between the two C 6 F 5 groups plays a pivotal role in controlling the intermolecular attractions. BF13 with a long and flexible tether might form a BF13 –fullerene sandwich complex that fails to prevent fullerene’s movement and aggregation, while BF5 with too short tether length decreases the possibility of interactions between the C 6 F 5 groups and the fullerenes. BF7 with the optimal tether length has the best ability to stabilize the morphology. In sharp contrast, the nonfluorinated BP7 analogue without C 6 F 5 –C 60 physical interactions does not have the capability of morphological stabilization, unambiguously revealing the necessity of the C 6 F 5 group. Most importantly, the function of BF7 can be also applied to the high-performance PffBT4BT-2OD:PC 71 BM system, which exhibited an original PCE of 8.80%. After thermal heating at 85 °C for 200 h, the efficiency of the PffBT4BT-2OD:PC 71 BM: BF7 device only decreased slightly to 7.73%, maintaining 88% of its original efficiency. To the best of our knowledge, this is the first time that the thermal-driven morphological evolution of the high-performance PffBT4BT-2OD polymer has been investigated, and its morphological stability in the inverted device can be successfully preserved by the incorporation of BF7 . This research also demonstrates that BF7 is not only effective with PC 61 BM but also to PC 71 BM.