Binary Organic Solar Cells with 19.2% Efficiency Enabled by Solid Additive

Abstract Morphology optimization is critical for achieving high efficiency and stable bulk‐heterojunction (BHJ) organic solar cells (OSCs). Herein, the use of 3,5‐dichlorobromobenzene (DCBB) with high volatility and low cost to manipulate evolution of the BHJ morphology and improve the operability and photostability of OSCs is proposed. Systematic simulations reveal the charge distribution of DCBB and its non‐covalent interaction with the active layer materials. The addition of DCBB can effectively tune the aggregation of PBQx‐TF:eC9‐2Cl during film formation, resulting in a favorable phase separation and a reinforced molecular packing. As a result, a power conversion efficiency of 19.2% (certified as 19.0% by the National Institute of Metrology) for DCBB‐processed PBQx‐TF:eC9‐2Cl‐based OSCs, which is the highest reported value for binary OSCs, is obtained. Importantly, the DCBB‐processed devices exhibit superior photostability and have thus considerable application potential in the printing of large‐area devices, demonstrating outstanding universality in various BHJ systems. The study provides a facile approach to control the BHJ morphology and enhances the photovoltaic performance of OSCs.