Halogen-free pyrazine additives enabling nonhalogenated <?A3B2 pi6?>solvent-processed organic solar cells with efficiency over 20%

The power conversion efficiency (PCE) of organic solar cells (OSCs) based on solid additive-processed active layers has seen rapid advancements. However, the widespread use of volatile halogenated additives poses notable environmental and health concerns. Here, by leveraging the electron cloud inhomogeneity of the pyrazine core, we enhanced intramolecular charge delocalization via the introduction of an electron-rich methylthio group, thereby introducing a halogen-free, commercialized volatile solid additive, 2-(methylthio)pyrazine (T-PZ). This molecular design allows the sulfur atom in T-PZ to interact with the cyano groups of Y6, thereby enhancing the crystallinity of small molecule acceptors and optimizing the molecular aggregation of both donor and acceptor phases. The resulting PM6:Y6-based OSCs achieved a record PCE of 19.42%, along with enhanced operational stability. Notably, T-PZ also exhibited excellent compatibility with various active layers (PM6:L8-BO, PM6:BTP-eC9, D18-Cl:N3, and PM6:BTP-TO2:AT-β2O), achieving a remarkable PCE of 20.14% in the PM6:BTP-TO2:AT-β2O devices processed with non-halogenated solvents.