Recent Advances in Polymorphism of Organic Solar Cells

As organic solar cells (OSCs) achieve notable advancements, a significant consensus has been highlighted that the device performance is intricately linked to the active layer morphology. With conjugated molecules being widely employed, intermolecular interactions exert substantial influence over the aggregation state and morphology formation, resulting in distinct molecular packing motifs, also known as polymorphism. This phenomenon is closely associated with processing conditions and exerts a profound impact on functional properties. Consequently, understanding the mechanisms underlying polymorphism formation and establishing a definitive correlation between polymorphism and photophysical behavior is crucial for driving high-performance OSCs. In this review, a comprehensive synthesis of recent developments is provided and emphasizing its pivotal role in the field of OSC polymorphism. The thermodynamic and kinetic principles governing polymorphism formation are examined. Then, representative polymorphisms are classified in OSC materials, segmenting them into homopolymers, copolymers, and IDTT- and BTP-based small molecules. Additionally, prevalent strategies are evaluated for manipulating polymorphism. This review culminates with an analysis of the critical effects of polymorphism on OSCs, including charge carrier characteristics, photovoltaic efficiency, and long-term stability. By offering novel perspectives and practical insights, this work seeks to guide future efforts in the morphological optimization of high-efficiency OSCs.