Propeller-Shaped Acceptors for High-Performance Non-Fullerene Solar Cells: Importance of the Rigidity of Molecular Geometry

This paper describes the synthesis and application of beta TPB6 and beta TPB6-C as electron acceptors for organic solar cells. Compound beta TPB6 contains four covalently bonded PDIs with a BDT-Th core at the beta-position. The free rotation of PDIs renders beta TPB6 with varying molecular geometries. The cyclization of beta TPB6 yields beta TPB6-C with high rigidity of the molecular geometry and enlarged conjugated skeleton. The inverted solar cells based on beta TPB6-C and PTB7-Th as the donor polymer exhibited the highest efficiency of 7.69% with V-oc of 0.92 V, J(sc) of 14.9 mAcm(-2), and FF of 0.56, which is 31% higher than that for beta TPB6 based devices. The larger fraction of beta TPB6-C and PTB7-Th than that of beta TPB6:PTB7-Th in a blend film takes a face-on orientation packing pattern for pi-systems that benefits the charge transport and hence higher PCE value than that for beta TPB6:PTB7-Th. It was also foundthat a proper DIO:DPE additive further enhances this trend, which results in an increase of the PCE value for beta TPB6-C:PTB7-Th while decreasing the PCE value for beta TPB6:PTB7-Th.