In addition to PDI and NDI units, a

In addition to PDI and NDI units, a few other novel buildingblocks have also been developed for polymer acceptors in thepast two years. Due to the well-conjugated structure andelectron-rich properties, cyclopenta-dithiophene (CPDT) and itsderivatives were widely used to construct p-type polymers[94–97]. Liu and coworkers developed a series of n-type buildingblocks with B N bridging units, which are isoelectronic andisosteric to the C–C units and show strong electron withdrawingproperty. Through replacing a C–C unit with a B N in CPDT,they developed a new CPDT analog building block, B Nbridged thienylthiazole (BNTT, Fig. 7) with decreased LUMOand HOMO energy levels [98]. The resulting polymers throughcopolymerizing BNTT unit with other electron poor units exhibited excellent electron transfer property. A series of BNTT-basedpolymers (Fig. 7) were synthesized and used as the acceptors inBHJ OSCs [99].