Planar Benzofuran Inside-Fused Perylenediimide Dimers for High VOC Fullerene-Free Organic Solar Cells

Abstract

Bulk heterojunction organic solar cells based on perylenediimide (PDI) derivatives as electron acceptors have afforded high power conversion efficiency (PCE) but still lagged behind fullerene-based analogs. Design of novel molecular structures by adjusting PDI ring and/or connection mode remains the breakthrough point to improve the photovoltaic performance. After introducing benzofuran at inside bay positions and linked with single bond and fluorene unit, mandatory planar PDI dimers were achieved and named as FDI2 and F-FDI2 respectively. Both acceptors show high-lying LUMO energy levels and gave high VOC beyond 1.0 V when using classic polymer of PBDB-T as electron donor. However, FDI2 and F-FDI2 gave totally different photovoltaic performance with PCEs of 0.15% and 6.33% respectively. The central fluorene linkage increased the miscibility of materials and ensured much higher short-circuit current due to the formation of suitable phase separation. Our results demonstrated that utilizing the mandatory planar skeleton of PDI dimers is simple and effective strategy to achieve high-performance non-fullerene electron acceptors, and the modulation of central conjugated units is also vital.