Recent advances of polymer acceptors for efficient all-polymer solar cells

All-polymer solar cells (all-PSCs) featuring a photo-active layer composed of a blend of p-type polymers as donors and n-type polymers as acceptors show superior operational stability and remarkable mechanical flexibility compared to conventional organic solar cells with n-type small molecules as acceptors. Although recent achievements have boosted the power conversion efficiencies of all-PSCs beyond 19%, further progress has been hampered by the lack of electron-deficient building blocks with optimized physicochemical properties and the slow evolution of polymer acceptors within the active layers. This review presents a comprehensive overview of the recent development of high-performing n-type polymer acceptors, systematically categorized into imide-functionalized polymers, amide-functionalized polymers, cyano-functionalized polymers, B ← N-embedded polymers, and polymerized small-molecule acceptors. Through a comprehensive analysis of structure-property-performance correlations, we illustrate the molecular design strategies that have proven effective in enhancing light absorption, charge mobility, and phase compatibility within donor-acceptor polymer networks. The review also identifies key challenges-such as reducing synthetic complexity, maintaining morphological stability, and minimizing energetic disorder-that must be addressed to fully realize the potential of all-PSCs. Ultimately, advancing the molecular engineering of polymer acceptors is pivotal for pushing the boundaries of efficiency, scalability, and long-term durability in all-PSCs.