A novel polymer donor with local stacking precise control fabricates flexible near-infrared organic photodetectors for health monitoring

Flexible organic photodetectors (OPDs) are pivotal for non-invasive wearable health monitoring. However, current flexible devices suffer from performance degradation during fabrication (compared to rigid counterparts) and insufficient mechanical/operational stability. To address these challenges, we develop a novel polymer donor, PBFPyT, by incorporating the thiadiazolo[3,4-c]pyridine (PyT) unit into the polymer backbone to enhance intermolecular interactions and mechanical compliance. This design enhances intermolecular interactions through denser π-π stacking, promoting local ordered packing to improve charge transport. Concurrently, the moderate backbone twisting increases conformational flexibility, facilitating stress dissipation via molecular entanglement within the blend film. The resulting polymer exhibits a reduced elastic modulus and increased tensile strain, providing sufficient mechanical compliance to support efficient photodetection performance and strain tolerance. Consequently, the flexible OPD retains near-complete photocurrent response relative to its rigid device (~96 %). Meanwhile, it achieves an ultra-low dark current density of 1.39 × 10⁻¹⁰ A cm⁻² and an ultra-high specific detectivity of 5.86 × 10¹³ Jones. Crucially, the PBFPyT-based flexible device maintains over 80 % of its initial detection performance after 1000 bending cycles. These results demonstrate the significant potential of PBFPyT for high-performance flexible photodetectors and wearable health monitoring systems.