n-Type Conjugated Polymers: Molecular Design, Material Properties, and Device Applications

Both n-type and p-type conjugated polymers play vital roles in the advancement and commercialization of polymer electronics. Through the tremendous efforts of scientists and engineers in this field over the past decade, n-type polymer semiconductors have experienced remarkable progress in nearly every aspect. However, most of the reported high-performance polymer semiconductors still exhibit p-type characteristics. The performance gap between p-type and n-type polymer semiconductors has become the Achilles' heel of polymer electronics, hindering the development of emerging applications such as logic circuits. Therefore, a timely and comprehensive overview of recent advances in the molecular design, material properties, and device applications of n-type conjugated polymers is essential to facilitate the development of high-performance n-type polymer materials. This review offers a comprehensive overview of recent advancements in n-type conjugated polymers, focusing on their fundamental optoelectronic properties, strategic molecular design, and emerging device applications. It starts by introducing the basic principles and historical background and highlighting both the importance and the challenge of developing effective n-type conjugated polymers. Subsequently, it systematically establishes structure-property relationships by first outlining key characteristics, including energy level, charge transport property, morphology, and mechanical property, and then correlates them with crucial molecular design strategies. This review also outlines the important applications and provides an overview of the critical progress in emerging optoelectrical devices, including organic solar cells and organic field-effect transistors. Finally, the challenges and promising research directions for n-type conjugated polymers are presented, which provide valuable guidance for the design of high-performance n-type polymer semiconductors and the exploration of more advanced applications in the future.