Perylene‐Diimide Dimers with Cross Conformations as Cathode Interfacial Layers for High‐Performance and Stable Thin‐Film Solar Cells

A series of PDI-based monomers and cross-coupled copolymers have been reported recently, exhibiting excellent photoelectric performance as cathode interfacial layers (CILs) in organic solar cells (OSCs). However, the problems of high crystallinity for monomers and poor batch-to-batch repeatability for copolymers are still unresolved, which inspire the probe to the size of PDI-based materials. Herein, PDI-based homo-oligomers, namely single-bond-linked perylene-diimide dimers (S-di(PDI)s) were designed and synthesized. Compared with PDI monomers, S-di(PDI)s not only retain the large planar conjugated backbone of PDI subunits, but also exhibit a cross conformation between two PDI blades, which is beneficial for maintaining excellent electron transporting capability while reducing intermolecular excessive aggregation and achieving outstanding optical and thermal stabilities. Among them, the binary devices of D18:L8-BO fabricated with S-di(PDI)-NBr CIL achieve a remarkable PCE of 20.53%, even higher than devices fabricated with copolymer PNDIT-F3N that is widely used as CIL in state-of-the-art OSC system. Meanwhile, perovskite solar cells (PSCs) based on S-di(PDI)-NBr CIL also achieved an outstanding PCE of 26.53%, much higher than PSCs based on C₆₀ CIL.