Ionized Phenanthroline Derivatives Suppressing Interface Chemical Interactions with Active Layer for High‐efficiency Organic Solar Cells with Exceptional Device Stability

Abstract The contact interface between the charge transport interlayer and the active layer is crucial for the non‐fullerene organic solar cells (NF OSCs) to achieve high efficiency and long‐term stability. In this study, two novel phenanthroline (Phen) derivatives, tbp ‐Phen and tbp ‐PhenBr, are developed as efficient cathode interfacial materials (CIMs). The larger steric hindrance substituents and the ionization of nitrogen atoms on the Phen framework jointly enable the tbp ‐PhenBr CIM with a stable film morphology and immensely suppress the detrimental interface chemical interactions with the NF active layer. Consequently, tbp ‐PhenBr‐based OSC achieves a higher efficiency (PCE = 16.34%) than bathocuproine (BCP)‐based control device (PCE = 13.70%) using PM6:Y6 as the active layer. More importantly, the tbp ‐PhenBr‐based device maintains 80% of its initial efficiency ( T 80 ) for 3264 h in dark conditions and 220 h after being heated at 85 °C, significantly outperforming the BCP‐based device. The tbp ‐PhenBr CIM also shows broad applicability across various binary and ternary active layer systems, affording a notable PCE of 19.49%. Additionally, the tbp ‐PhenBr CIM can be processed via a thermal evaporation technique and the prepared devices exhibit high reproducibility. This work provides innovative insights into the molecular design of the CIMs for stable and efficient NF OSCs.