Thermodynamic Nucleation‐Guided Alloy‐Like Non‐Fullerene Blends Enabling Morphology‐Driven Intra‐Moiety Excited State Dynamics for High‐Performance Near‐Infrared Organic Photodetectors

Y6‐series non‐fullerene acceptors (NFAs) promise numerous opportunities in organic optoelectronics owing to their ability to generate intra‐moiety excited (i‐EX) states, which enable efficient charge separation within NFA domains. However, fully exploiting the benefits of the i‐EX mechanism requires highly crystalline and uniform morphologies, which are difficult to achieve in Y6‐based blends due to uncontrolled aggregation. Here, a thermodynamically guided nucleation control strategy is introduced to optimize bulk heterojunction morphology for optimal i‐EX activation. The nucleation energy threshold of the PTB7‐Th:Y6 blend is lowered by incorporating a small amount of L8BO‐F, which possesses a lower nucleation energy barrier than Y6, as a crystallization seed. This modulates early‐stage nucleation to form an alloy‐like blend comprising uniformly distributed, highly crystalline, and pure NFA domains across the film. The controlled crystallization facilitates long‐range exciton delocalization and enhances i‐EX–mediated charge generation and transport, as evidenced by faster i‐EX formation and more rapid transition to charge‐separated states in the alloy‐like blend. As a result, organic photodetectors based on the optimized alloy‐like NFA system exhibit a high specific detectivity of 1.44 × 10 11 Jones at 800 nm with fast temporal response, highlighting the potential of morphology‐controlled i‐EX dynamics for high‐sensitivity and high‐speed near‐infrared detection.