Achieving a Record Fill Factor of Approaching 84% and 21% Efficiency in Binary Organic Solar Cells via Solid Additive Engineering

ABSTRACT Solid additives, as an efficient approach of morphology control in organic solar cells (OSCs), remain not fully understand in terms of the influence of their intermolecular interactions with photoactive molecules on morphological evolution and ultimate device performance. Herein, the intermolecular interactions between solid additives and photoactive molecules were precisely tuned through molecular isomerization engineering. Three isomers of iodine‐substituted 1,2,4‐trichlorobenzene were adopted as the solid additives. The four strongly electronegative halogen atoms readily produce intense interactions with the photoactive materials, thereby enhancing their J ‐type stacking and broadening the absorption spectrum. Crucially, the iodine substituent position on the solid additives was altered, which improved their miscibility and intermolecular interactions with photoactive materials, forming a bicontinuous interpenetrating network. Consequently, the binary OSCs achieved an impressive fill factor of approximately 84% with an efficiency of nearly 21% (certified as 20.42%), ranking among the top OSC performances to date. Furthermore, the device demonstrated excellent storage stability, with an extrapolated T 80 (maintaining 80% of its initial efficiency) exceeding 10 000 h.