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DOI: 10.1002/adma. 201504120 separation and transfer, and ultimately achieve superior photovoltaic properties.[25] It is important to note that nonplanar molecular geometry is essential even in fused PDIs to ensure forming a bicontinuous network with donor materials in BHJ.[26] Consequently, ideal PDI acceptors should possess enhanced conjugation and molecular packing order for improving charge mobility, while maintaining nonplanar structure to be able to suppress the formation of large aggregates. Therefore, the ability to modulate molecular geometry of PDI acceptors with appropriate twist angle is critical. By introducing a heteroatom into a conjugated system, it can expediently alter its molecular skeleton and electronic properties.[27] Therefore, the exploration of rigid fused PDI dimers with heteroaromatic bridges can be a fruitful avenue for developing efficient n-type materials for nonfullerene OPVs. The numbers of potential scaffolds that can be generated by varying different heteroatoms will also facilitate the discovery of optimal molecular geometry for improving BHJ morphology. Semiflexible PDI-T (Figure 1a) in which two PDI moieties are linked by a thiophene through single bond, has been reported as an acceptor exhibiting modest efficiency in devices.[14] To improve its effectiveness as an acceptor, we have developed a novel fused derivative FPDI-T through the oxidative cyclization of PDI-T. The electron-rich thiophene helps tuning the overall electron distribution in the fused structure while the five-membered ring creates a nonplanar skeleton. Compared to PDI-T, fused FPDI-T shows increased effective π-conjugation and …