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 (T₈₀) 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.