Suppression of Deep-Level Defects Enabled by a Ternary Strategy for Ultralow Dark Current Near-Infrared Organic Photodetectors

Near-infrared (NIR) organic photodetectors (OPDs) hold significant promise for emerging applications such as wearable health monitoring, optical communication, and machine vision; however, their performance is often constrained by high dark current density arising from deep-level defects, which impedes the detection of faint optical signals and creates a critical bottleneck for precise biohealth monitoring. This work reports an effective ternary blend strategy by incorporating the high-crystallinity polymer acceptor PY-IT into a PM6:Y6-HU binary system to engineer the active layer morphology via the passivation of energetic disorder and structural defects. Comprehensive morphological and electronic characterizations reveal the multitiered mechanism of dark current suppression; thermodynamically, PY-IT modulates surface energy to drive vertical phase separation, optimizing interface contact, and structurally, it acts as a nucleation template to enhance molecular packing and increase crystal coherence length (CCL). Furthermore, trap density of states (tDOS) derived from capacitance-frequency measurements confirms that this nanostructural reconstruction significantly suppresses the formation of deep-level electronic trap states. By severing the primary pathway for trap-assisted thermal generation, the device intrinsic noise is fundamentally mitigated. As a result, the ternary OPD device achieves high performances with an ultralow Jd of 1.57 × 10–11 A cm–2 at 0 V and high specific detectivity (Dsh*) of 2.12 × 1014 Jones at 800 nm and OPD arrays were fabricated with ternary systems, which demonstrates high performances and excellent uniformity for applications in photoplethysmography (PPG). This study establishes a rigorous logic connecting trap density reduction to macroscopic performance, providing a robust paradigm for next-generation wearable health monitors.