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 × 10¹¹ 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.