Recent development in solid additives enables high-performance organic solar cells

The active layer morphology in organic solar cells (OSCs) including ideal vertical phase separation, molecular packing, and domain size are crucial in influencing the behavior of excitons and charge carriers. Many techniques have been developed to optimize the morphology throughout fabrication extending from thermal and solvent vapor annealing to incorporation of solvent additives. Nevertheless, these posttreatments are unsuitable for large-area OSC fabrication, and solvent additives remain within the active layer, gradually comprising morphology and device performance over time. Recently, the development of solid additives with their unique characteristics, offers superior morphology control, easy posttreatments, and enhanced device stability. Consequently, solid additives have rapidly achieved popularity as a universal and considerably used method to optimize morphology and performance. However, the operational mechanism of solid additives, especially their interactions with donor-acceptor within the active layer remains unclear, hindering their development and use in emerging OSC systems. Therefore, we have summarized recent findings on solid additives volatile and nonvolatile depending on their characteristics, and a comprehensive discussion of different mechanisms is reviewed. These insights aim to assist in choosing suitable solid additives for newly developed OSC systems. Finally, we provide a brief overview of challenges and potential advancements concerning solid additives in OSCs.