Mediating morphology evolution via the regulation of molecular interactions between volatile solid additives and electron acceptor to enable organic solar cells with 19.20% efficiency

Regulating the morphology of the active layer is crucial for achieving high-efficiency organic solar cells (OSCs). However, due to weak intermolecular interactions, organic conjugated polymers often exhibit low structural order, leading to poor microstructure morphology, limited charge transport, and increased charge recombination. Herein, solid but volatile additive 1, 8-dibromonaphthalene (DBN) is first employed to regulate intermolecular interactions and manipulate the evolution of the microstructure morphology in D18:L8-BO based blend films. DBN is present during solution casting but fully volatilizes after thermal annealing processing. The superior miscibility and remarkably strong intermolecular interaction between DBN and L8-BO promote the formation of a more orderly stacking, reduce it-it stacking d-spacing with enhanced crystalline coherence length, and create a smoother surface with smaller aggregation domains. As a result, the DBN-treated blend film exhibits more efficient charge transport and reduced charge recombination and the corresponding OSC device delivers a dramatically increased PCE from 17.63% to 19.20% with simultaneously enhanced short-circuit current (JSC) and fill factor (FF). This study provides experimental evidence demonstrating that volatile halide solid additives can effectively control morphological evolution by utilizing the superior miscibility and strong interaction between additives and active materials, highlighting their potential in the fabrication of high-efficiency OSCs.