Morphological Stabilization by Supramolecular Perfl uorophenyl-C60 Interactions Leading to Effi cient and Thermally Stable Organic Photovoltaics

A new PC61BM-based fullerene, [6,6]-phenyl-C-61 butyric acid pentafluorophenyl ester (PC61BPF) is designed and synthesized. This new n-type material can replace PC61BM to form a P3HT:PC61BPF binary blend or serve as an additive to form a P3HT:PC61BM:PC61BPF ternary blend. Supramolecular attraction between the pentafluorophenyl group of PC61BPF and the C-60 cores of PC61BPF/PC61BM can effectively suppress the PC61BPF/PC61BM materials from severe aggregation. By doping only 8.3 wt% PC61BPF, device PC(61)BP(F)651 exhibits a PCE of 3.88% and decreases slightly to 3.68% after heating for 25 h, preserving 95% of its original value. When PC61BP with non-fluorinated phenyl group is used to substitute PC61BPF, the stabilizing ability disappears completely. The efficiencies of PC(61)BP651 and PC(61)BP321 devices significantly decay to 0.44% and 0.11%, respectively, after 25 h isothermal heating. Most significantly, this strategy is demonstrated to be effective for a blend system incorporating a low band-gap polymer. By adding only 10 wt% PC61BPF, the PDTBCDTB:PC71BM-based device exhibits thermally stable morphology and device characteristics. These findings demonstrate that smart utilization of supramolecular interactions is an effective and practical strategy to control morphological evolution.