A green solvent processable, self‐doped N‐annulated perylene butyl tetraester applied as a solar cell cathode interlayer

Abstract We report a new amino‐bay‐substituted, N‐annulated perylene butyl tetraester (NH 2 ‐PTEN‐H) with application as a cathode interlayer in organic photovoltaic devices. Synthesis from the parent N‐annulated perylene butyl tetraester is presented alongside comprehensive structural characterization. Density functional theory calculations on NH 2 ‐PTEN‐H and related analogues, both with and without N‐annulation and amino‐bay substitution, show that N‐annulation locks the perylene core into a planar conformation even in the presence of a sterically demanding amino group. Steady‐state optical spectra reveal intramolecular charge transfer characteristics and a large excited‐state dipole moment. Solubility profiling establishes perylene butyl tetraesters as a highly soluble subclass of perylene dyes; NH 2 ‐PTEN‐H, in particular, dissolves readily in the green solvent ethyl acetate up to 168 mg mL −1 , enabling environmentally benign ink formulations. These inks were spin‐coated into uniform thin films on quartz and studied, and electron paramagnetic resonance spectroscopy confirmed NH 2 ‐PTEN‐H as a paramagnetic species in the solid state. Utilized as a cathode interlayer in conventional organic photovoltaic devices, architectures containing NH 2 ‐PTEN‐H deliver power conversion efficiencies comparable to those using the benchmark cathode interlayer material PFN‐Br. © 2025 The Author(s). Polymer International published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.