High‐Performance Small Molecule Organic Solar Cells Enabled by a Symmetric‐Asymmetric Alloy Acceptor with a Broad Composition Tolerance

Abstract Using a combinatory blending strategy is demonstrated as a promising path for designing efficient organic solar cells (OSCs) by boosting the short‐circuit current density and fill factor. Herein, a high‐performance ternary all‐small molecule OSC (all‐SMOSCs) using a narrow‐bandgap alloy acceptor containing symmetric and asymmetric molecules (BTP‐eC9 and SSe‐NIC) and a wide‐bandgap small molecule donor MPhS‐C2 is reported. Introducing the synthesized SSe‐NIC into the MPhS‐C2:BTP‐eC9 host system can broaden the absorption spectrum, modulate energy offsets, and optimize the molecular packing of the host materials. After systematically optimizing the weight ratio of MPhS‐C2:BTP‐eC9:SSe‐NIC, a champion efficiency of 18.02% is achieved. Impressively, the ternary system not only delivered a broad composition tolerance with device efficiencies over 17% throughout the whole blend ratios, but also exhibited less non‐geminate recombination and energy loss, and better‐light‐soaking stability than the corresponding binary systems. This work promotes the development of high‐performance ternary all‐SMOSCs and heralds their brighter application prospects.