Achieving 20% Efficiency in Organic Solar Cells Through Conformationally Locked Solid Additives

Abstract Volatile solid additives (VSAs) have emerged as one of the most effective strategies for optimizing the active layer morphology of organic solar cells (OSCs). In this study, two VSAs, HBT‐1 and HBT‐2, are designed and synthesized to investigate the effect of the VASs’ conformation on the photovoltaic performances. Compared to HBT‐1, HBT‐2 incorporates internal noncovalent conformational locks (NoCLs), resulting in reduced conformational disorder, improved molecular planarity, and enhanced crystallinity. These features significantly influence the intermolecular packing of both donor and acceptor materials in the active layer, which can facilitate charge transport and reduce charge recombination. Consequently, the D18:L8‐BO:PY‐C11 OSCs utilizing the HBT‐2 additive achieved an impressive efficiency of 20.01%, markedly higher than devices fabricated without additives (17.83%) and those processed with HBT‐1 (18.76%). Furthermore, HBT‐2 demonstrated excellent compatibility across multiple systems. This work underscores the NoCL strategy as a straightforward and effective approach for designing VSAs for high performance OSCs.