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 intermolecular π-π stacking between the flanking terminal groups. The twist angle between the aryl substituent and INCN unit has a significant influence on the π-π stacking distance of terminal unit. IDT-IC-T with a smaller twist angle has a shorter π-π stacking 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 (1.47×10−4 cm2 V−1 s−1) and the best power conversion efficiency (PCE) of 9.43%. As for IDT-IC, which only shows an electron mobility of 7.33×10−5 cm2 V−1 s−1 and a PCE of 5.82%. These findings provide a facile and effective way to improve the photovoltaic performance.