The Emerging Role of Solid Additives in Advancing Stability and Performance of Organic Solar Cells

The rapid development of organic solar cells (OSCs) in recent years has been largely driven by advances in nonfullerene acceptors and innovative device architectures. Beyond material design, solid additives have emerged as an effective strategy to regulate active‐layer morphology, enhance charge transport, and suppress recombination losses, thereby improving device efficiency and stability. Compared with traditional solvent additives, solid additives provide better control over nanoscale molecular packing and donor–acceptor phase separation, leading to more stable film morphologies. This review summarizes recent progress on solid additives in OSCs, focusing on their impact on active‐layer crystallinity, donor–acceptor miscibility, exciton dissociation, and charge‐carrier dynamics. Representative studies demonstrate that solid additives can significantly enhance power conversion efficiency by promoting favorable molecular orientation and reducing trap‐assisted recombination. Their role in mitigating key challenges such as nonradiative voltage losses, thermal instability, and large‐area film uniformity is also discussed. Furthermore, different classes of solid additives, including volatile small molecules, halogenated compounds, and emerging green materials, are compared in terms of performance enhancement and scalability. Finally, future perspectives emphasize rational additive design to enable eco‐friendly, durable, and commercially viable OSC technologies.