Conjugated Polymer‐Halogenated Alkane Synergy: 19.37% Efficiency in Binary Organic Solar Cells

ABSTRACT The morphological instability of the active layers remains a critical bottleneck limiting the photovoltaic performance and long‐tern operational stability of organic solar cells (OSCs). In this work, the synergistic mechanism of the conjugated polymer PM6 and halogenated alkane additive 1,8‐diiodooctane (DIO) was systematically investigated to understand the effect on the microstructure and photovoltaic performances of the D18:BTP‐BO‐4F‐based OSCs active layer. The results demonstrate that the co‐introduction of PM6 and DIO effectively refines the phase separation morphology, modulates donor‐acceptor molecular aggregation, and promotes favorable nanoscale domain connectivity. This synergistic approach not only enhances the carrier transport and extraction but also significantly inhibits both monomolecular and bimolecular recombination losses. Consequently, the power conversion efficiency of the binary OSCs increases from 16.68% to 19.37%, accompanied by an open circuit voltage of 0.882 V, a short‐circuit current density of 28.45 mA cm ⁻² , and a fill factor of 77.14%. Furthermore, devices fabricated using this synergistic strategy retain over 90% of their initial efficiency after 60 d of storage under inert atmospheric conditions. These findings underscore the critical role of the conjugated polymer‐additives synergy in directing active layer morphology regulation, thereby offering a robust and scalable strategy for concurrently improving the efficiency and stability of OSCs.