The Effects of Polymer Molecular Weight on Morphology and the Device Efficiency: Progress and Prospects for Organic Solar Cells

Abstract Organic solar cells (OSCs) are developing as a crucial technology for sustainable energy, attaining power conversion efficiencies (PCEs) of over 20%. The morphology of the active layer is essential in influencing PCE, but its exact manipulation is difficult because of the complex interactions between donor and acceptor molecules. The molecular weight ( M w ) of polymers is a crucial parameter that significantly affects morphological development, including domain size, purity, crystallinity, and molecular orientation. Here the trade‐offs of M w regulation are examined, emphasizing that high‐ M w polymers improve stability and crystallinity but may hinder phase separation. In contrast, low‐ M w polymers promote finer phase separation at the cost of mechanical integrity. Moreover, current achievements are synthesized to clarify methodologies for optimizing M w to achieve balanced morphological features, to enhance active layer design, and maximize the potential of OSCs. These insights facilitate the resolution of existing difficulties and promote the advancements of OSCs toward useful and sustainable applications.