Enhance the performance of polymer solar cells via extension of the flanking end groups of fused ring acceptors

Two new fused ring electron acceptors（FREAs）IDT-IC-T and IDT-IC-B with thienyl or phenyl substituents at the terminal INCN unit are synthesized.Theoretical calculations indicate that the two acceptors dominantly favor an intermolecularπ-πstacking between the flanking terminal groups.The twist angle between the aryl substituent and INCN unit has a significant influence on theπ-πstacking distance of terminal unit.IDT-IC-T with a smaller twist angle has a shorterπ-πstacking distance than that of IDT-IC-B with a larger twist angle.In addition,extending the conjugation also affects the blend film morphology.IDT-IC-T and IDT-IC-B based photoactive films show appropriate nanoscale phase separations;whereas,blend films based on the parent compound IDT-IC show large-size acceptor domains.As expected,PBDB-T:IDT-IC-T blend films show higher and more balanced electron and hole mobilities.Moreover,these two acceptors present a good charge-transport connectivity arising from the extended conjugation and the increased intermolecular overlapping.Ultimately,IDT-IC-T demonstrates the highest electron mobility(1.47×10;cm;V;s;)and the best power conversion efficiency（PCE）of 9.43%.As for IDT-IC,which only shows an electron mobility of 7.33×10;cm;V;s;and a PCE of 5.82%.These findings provide a facile and effective way to improve the photovoltaic performance.