Unfused-ring Acceptors with Dithienobenzotriazole Core for Efficient Organic Solar Cells

In recent years, non-fullerene acceptors (NFAs) with unfused-ring structure have received extensive attention due to their flexible combination of building blocks and relatively simple synthetic routes. In this work, three new A-D-C-D-A type unfused-ring acceptors (UFAs), named DTBTzEH-IC2F, DTBTzMe-IC2F and DTBTzMe-IC2Cl, were designed and synthesized with dithienobenzotriazole (DTBTz) as the core. Through modification of alkyl chain on the DTBTz unit and change of halogen atoms on the cyanoindanone end groups, the differences in optoelectronic properties of these three small molecule acceptors were investigated. The results show that changes in alkyl chain and halogen atom endow UFAs with different features, including shift in absorption, changes in energy level and molecular packing. When blended with donor PBDB-T, the organic solar cell based on DTBTzMe-IC2Cl achieves the highest device efficiency of 12.3%, while DTBTzEH-IC2F-based device obtains 11.5% efficiency and DTBTzMe-IC2F-based device obtains 12.0% efficiency. The stability tests show that all the devices obtain good efficiency retention rates. These results demonstrate that the introduction of a rigid aromatic ring DTBTz as an intermediate core not only effectively results in highly planar A-D-C-D-A small molecules, but also provides a new reference for the design and development of UFAs in OSCs.