Dual‐Asymmetric Solid Additive Enables Eco‐friendly All‐Polymer Solar Cells with Over 19 % Efficiency and Excellent Stability

Abstract The optimization of morphology in all‐polymer solar cells (all‐PSCs) often relies on the use of solvent additives. However, their tendency to remain trapped in the device due to high boiling points leads to performance degradation over time. In this study, we introduce a novel approach involving the design and synthesis of one dual‐asymmetric solid additive featuring mono‐brominated‐asymmetric dithienothiophene (SL‐1). Leveraging the synergistic effects of asymmetric substitution and core structures, fine‐tuning the molecule dipole moment enhancing solid additive interactions with host materials, thereby regulating polymer aggregation and influencing blend morphology during device fabrication. This results in highly ordered π–π stacking and a favorable phase‐separated morphology within all‐polymer active layer. Our work achieved a record efficiency of 19.19 % in eco‐friendly all‐PSCs, significantly outperforming SL‐0 (18.37 %) and SL‐2 (16.60 %), both featuring an asymmetric core. Furthermore, SL‐1‐treated all‐PSCs retain over 90 % of their initial efficiency after 2140 hours of operation, with an extrapolated T80 lifetime reaching 12400 hours. This represents a significant improvement in stability compared to devices treated with solvent additive (1‐CN), which typically exhibits a T90 lifetime of 700 hours. Our findings underscore the efficacy of utilizing dual‐asymmetric solid additives as a straightforward and viable strategy for optimizing all‐polymer morphology. SL‐1 represents a promising advancement towards eco‐friendly fabrication and application of high‐efficiency and stable all‐PSCs.