Recent Advances, Design Guidelines, and Prospects of All-Polymer Solar Cells

All-polymer solar cells (all-PSCs) consisting of polymer donors (P_Ds) and polymer acceptors (P_As) have drawn tremendous research interest in recent years. It is due to not only their tunable optical, electrochemical, and structural properties, but also many superior features that are not readily available in conventional polymer-fullerene solar cells (fullerene-PSCs) including long-term stability, synthetic accessibility, and excellent film-forming properties suitable for large-scale manufacturing. Recent breakthroughs in material design and device engineering have driven the power conversion efficiencies (PCEs) of all-PSCs exceeding 11%, which is comparable to the performance of fullerene-PSCs. Furthermore, outstanding mechanical durability and stretchability have been reported for all-PSCs, which make them stand out from the other small molecule-based PSCs as a promising power supplier for wearable electronic devices. This review provides a comprehensive overview of the important work in all-PSCs, in which pertinent examples are deliberately chosen. First, we describe the key components that enabled the recent progresses of all-PSCs including rational design rules for efficient P_Ds and P_As, blend morphology control, and light harvesting engineering. We also review the recent work on the understanding of the stability of all-PSCs under various external conditions, which highlights the importance of all-PSCs for future implementation and commercialization. Finally, because all-PSCs have not yet achieved their full potential and are still undergoing rapid development, we offer our views on the current challenges and future prospects.