NFAs show excellent synthetic flexi

NFAs show excellent synthetic flexibility with readily availablesource materials, which affords easily tunable optical/electronicproperties and improved solubility. NFAs can be tailored to pairwith novel polymer donors in terms of both optical complementarity and energetic compatibility, allowing OSCs to achievebroad spectrum coverage. In addition, the low-cost cores, facilesynthesis, and simplified purification can significantly reducethe production cost of NFAs. NFAs may overcome the high synthetic complexity of fullerenes, which benefits for the large-scaleproduction and commercialization. Early in 2011, Landi and hiscoworkers quantified the life cycle embodied energy of C60 andC70 fullerenes from cradle-to-grave, including the contributionsfrom synthesis, separation, purification, and functionalizationprocesses [185]. In the recent review article by Yan’s group, synthetic complexity of NFAs has also been discussed [37]. Here webriefly state the synthesis of some well-performing NFAs, i.e., several PDI derivatives and A–D–A type IDT-based NFAs. For example, the well-performing PDI derivative TPH–Se can besynthesized in five steps with a total yield of 55% [125]. APDI trimer-based small molecular acceptor Ta-PDI can beachieved through three steps synthetic procedure with a totalyield of 11% [119]. The A–D–A type acceptor normally needsmore steps to achieve than rylene derivatives. The synthesis ofITIC requires eleven steps to complete, with a total yield of