Benzobisthiazole and rhodanine based low energy level small molecule donors for organic solar cells

At present, high-performance small molecule donors for organic solar cells (OSCs) are almost entirely composed of the electron donating core benzodithiophene (BDT), which has resulted in a lack of material diversity and further improvement. In this article, we constructed an A-π-A′-π-A conjugated structure using electron withdrawing group benzobisthiazole (BBT) core and rhodanine end group, and synthesized two small molecule donors BBTSM-3 and BBTSM-4. Under the dual electron withdrawing effects of BBT and rhodanine, the HOMO energy levels of BBTSM-3 and BBTSM-4 reached extremely low levels (−5.60 eV and −5.64 eV), but still matched well with the acceptor Y6. In addition, through reasonable side chain regulation, BBTSM-3 exhibited stronger crystallinity and weaker aggregation at the same time. This provides a reference point for the use of the electron withdrawing core and the regulation of side chains among small molecule donors. Benzobisthiazole and rhodanine construct small molecule donors with A-π-A′-π-A molecular charge transport system and really low HOMO energy levels. • Benzobisthiazole and rhodanine were used to synthesize small molecule donors with A-π-A′-π-A system. • BBTSM reached really low HOMO energy levels, while still exhibited good exciton dissociation with Y6. • Stronger crystallinity and weaker aggregation can be achieved simultaneously by regulating the side chains.