Advancing all-polymer solar cells with solid additives

All-polymer solar cells (all-PSCs) have attracted significant research attention in recent years, primarily due to their advantages of outstanding photo-thermal stability and excellent mechanical flexibility. However, all-PSCs typically exhibit complex morphologies during the film formation of blend films, primarily due to the tendency to become entangled in polymer chains, negatively impacting their fill factor (FF) and morphology stability. Therefore, the optimization of the morphology of the co-mingled heterojunction is crucial for improving device performance. Recent studies reveal that solid additives (SAs) can realize the excellent regulation of the molecular aggregation state, molecular packing, and domain size of the active layer, which not only improves the exciton dissociation, charge transport and collection process of the device but also ultimately realizes the enhancement of the device efficiency. Therefore, this review provides an in-depth insight into the different mechanisms of solid additives in all-PSCs, offering a comprehensive discussion on the research progress in optimizing the morphology and enhancing morphology stability. Finally, we present an outlook for the further structural modification strategies of solid additives towards better bulk morphology and stability of all-PSCs, paving the way for achieving excellent photo-thermal stability, superior mechanical flexibility, and high-efficiency all-PSCs.