Electron Acceptors Based on α-Substituted Perylene Diimide (PDI) for Organic Solar Cells

Perylene diimide (PDI) derivatives functionalized at the ortho-position (alpha PPID, alpha PBDT) were synthesized and used as electron acceptors in non-fullerene organic photovoltaic cells. Because of the good planarity and strong pi-stacking of ortho-functionalized PDI, the alpha PPID and alpha PBDT exhibit a strong tendency to form aggregates, which endow the materials with high electron mobility. The inverted OPVs employing alpha PDI-based compounds as the acceptors and PBT7-Th as the donor give the highest power conversion efficiency (PCE) values: 4.92% for alpha PBDT-based devices and 3.61% for alpha PPID-based devices, which are, respectively, 39% and 4% higher than that of their beta-substituted counterparts beta PBDT and beta PPID. Charge separation studies show more efficient exciton dissociation at interfaces between alpha PDI-based compounds and PTB7-Th. The results suggest that alpha-substituted PDI derivatives are more promising electron acceptors for organic photovoltaic (OPV) components than beta-isomers.