Intrinsic Role of Volatile Solid Additive in High‐Efficiency PM6:Y6 Series Nonfullerene Solar Cells

Abstract Organic nonfullerene solar cells (ONSCs) have made unprecedented progress; however, morphology optimization of ONSCs is proven to be particularly challenging relative to classical fullerene‐based devices. Here, a novel volatile solid additive (VSA), 2‐hydroxy‐4‐methoxybenzophenone (2‐HM), is reported for achieving high‐efficiency ONSCs. 2‐HM functions as a universal morphology‐directing agent for several well‐known PM6:Y6 series nonfullerene blends, viz. PM6:Y6, PM6:BTP‐eC9, PM6:L8‐BO, leading to a best efficiency of 18.85% at the forefront of reported binary ONSCs. VSAs have recently emerged, while the intrinsic kinetics is still unclear. Herein, a set of in situ and ex situ characterizations is employed to first illustrate the molecule‐aggregate‐domain transition dynamic process assisted by the VSA. More specifically, the role of 2‐HM in individual donor PM6 and acceptor Y6 systems is unlocked, and the function of 2‐HM in altering the PM6:Y6 bulk heterojunction blends is further revealed for enhanced photovoltaic performance. It is believed that the achievement brings not only a deep insight into emerging volatile solid additive, but also a new hope to further improve the molecular ordering, film microstructure, and relevant performance of ONSCs.