Tuning the intermolecular interaction of A2-A1-D-A1-A2 type non-fullerene acceptors by substituent engineering for organic solar cells with ultrahigh VOC of ~1.2 V

For non-fullerene acceptors (NFAs) with linear A2-A1-D-A1-A2 backbone, there are three kinds of possible intermolecular interaction, A1-A1, A1-A2 and A2-A2 stacking. Hence, it is a huge challenge to control this interaction and investigate the effect of intermolecular stacking model on the photovoltaic performance. Here, we adopt a feasible strategy, by utilizing different substituent groups on terminal A2 unit of dicyanomethylene rhodanine (RCN), to modulate this stacking model. According to theoretical calculation results, the molecule BTA3 with ethyl substituent packs via heterogeneous interaction between A2 and A1 unit in neighboring molecules. Surprisingly, the benzyl group can effectively transform the aggregation of BTA5 into homogeneous packing of A2-A2 model, which might be driven by the strong interaction between benzyl and A1 (benzotriazole) unit. However, different with benzyl, phenyl end group impedes the intermolecular interaction of BTA4 due to the large steric hindrance. When using a BTA-based D-π-A polymer J52-F as donor according to “Same-A-Strategy”, BTA3-5 could achieve ultrahigh open-circuit voltage ( V OC) of 1.17–1.21 V. Finally, BTA5 with benzyl groups realized an improved power conversion efficiency (PCE) of 11.27%, obviously higher than that of BTA3 (PCE=9.04%) and BTA4 (PCE=5.61%). It is also worth noting that the same trend can be found when using other four classic p-type polymers of P3HT, PTB7, PTB7-Th and PBDB-T. This work not only investigates the intermolecular interaction of A2-A1-D-A1-A2 type NFAs for the first time, but also provides a straightforward and universal method to change the interaction model and improve the photovoltaic performance.