Acceptor Crystallinity Engineering Enables >20% Efficiency Binary Organic Solar Cells with 83.0% Fill Factor.

For spontaneously crystallized organic photovoltaic materials, morphology optimization remains a challenge due to the disparity in crystallinity between the donor and acceptor components. Imperfections in the crystalline phases result in significant trap-assisted recombination, which emerges as a critical factor limiting the fill factor (FF) of organic solar cells (OSCs). Herein, a method is introduced for precise regulation of the acceptor crystallinity, utilizing a novel upper-layer acceptor processing solvent, trichloroethylene (TCE), to improve the state and vertical morphology of the active layer. The TCE solvent synergistically optimizes intermolecular interactions among acceptor molecules and balances the film-forming process, thereby increasing the proportion of transport phases and forming high-speed channels for electron transport, which subsequently reduces trap-assisted charge recombination. As a result, the photovoltaic efficiency of binary organic solar cells reaches 20.05%. More importantly, an unprecedented FF of 83.0% is obtained, representing the highest FF value for OSCs. This facile and effective approach offers a promising means for constructing efficient charge transport networks and fabricating high-efficiency and morphologically stable OSCs.