Phenol‐Functionalized Perylene Bisimides as Amine‐Free Electron Transporting Interlayers for Stable Nonfullerene Organic Solar Cells

Abstract A new type of cathode interlayer composed of 2,6‐di‐ tert ‐butyl‐phenol‐functionalized perylene bisimide (PBI‐2P) is successfully applied as an electron transporting layer for fused‐ring nonfullerene organic solar cells (OSCs). The stable contact between these novel electron transporting layers and the representative nonfullerene acceptor Y6 greatly enhances the device stability compared to conventional amine‐group containing cathode interlayers. Moreover, the easily formed biradical species in the interlayers yields rather good thickness tolerance of the PBI‐2P layer in photovoltaic devices. The OSCs based on the PBI‐2P interlayer show a power conversion efficiency up to 17.20% and good stability compared to amino‐group functionalized interlayers. The findings demonstrate a promising design principle for cathode interlayer engineering based on pigment chromophores equipped with the 2,6‐di‐ tert ‐butylphenoxy groups that are prone to form the respective ultrastable butylphenoxy radicals for stable nonfullerene OSCs.