Facile-processed n-p-type binary cathode interlayers: Concurrent enhancement of photovoltaic performance and mechanical robustness

n-Type small molecules such as perylene diimides (PDI) and naphthalene diimides (NDI) derivatives are widely used as cathode interlayers (CILs) in organic solar cells (OSCs) employing narrow-band gap electron acceptors (NBGEAs), owing to their excellent electron transport properties. However, such interfacial materials tend to severely aggregate within the film, leading to poor film morphology and mechanical fragility. Moreover, these CILs often pin the cathode Fermi level at energies lower than the electron transport levels of NBGEAs, leading to suboptimal energy level alignment. In this study, we introduce a binary n-p-type CIL by incorporating the classical p-type cathode interfacial material PFN-Br into the n-type cathode interfacial material PDINO. The resulting binary CIL exhibits a modified PDINO aggregation configuration and a smoother film morphology, while it also effectively lowers the cathode work function through the PFN-Br induced double dipole effect. These combined effects enhance and stabilize the electrical properties of the binary CIL. Model OSCs based on PM6: Y6 utilizing this n-p type CIL show suppressed bimolecular and trap assisted recombination, resulting in improved photovoltaic performance. Additionally, the binary CIL enhances the mechanical durability of flexible devices, highlighting its potential for application in high-performance rigid and flexible OSCs.