Simultaneous Enhancement of Narrowband Detection and Suppression of Dark Current in Organic Near‐Infrared Photodetectors via Second‐Order Resonant Microcavity

Near‐Infrared Organic Photodetectors (NIR‐OPDs) have garnered attention for their cost‐effective solution‐processability and unlimited molecular tunability. Recently, microcavities are integrated into NIR‐OPDs to enhance the weak absorption of charge transfer (CT) states in organic blends. These Microcavity‐Enhanced Near‐Infrared Organic Photodetectors (MC‐NIR‐OPDs) exhibit superior narrowband detection capabilities and broad application potential. However, conventional first‐order cavity modes suffer from parasitic absorption, limiting responsivity (R). Here, utilizing a second‐order resonance mode is proposed to enhance the absorption of CT states in a model system: the PM6:Y6 blend. By integrating a metal‐ dielectric (M‐D) resonant microcavity into a thick bulk heterojunction (BHJ) OPD structure, the device achieves a remarkable 13 nm full‐width at half‐maximum (FWHM) and a peak external quantum efficiency (EQE) of up to 34.7% at the operating wavelength of 960 nm, significantly outperforming previous reports on PM6:Y6‐based OPDs. Concurrently, a substantial reduction in dark current to 8.4 nA cm −2 is observed, and the detectivity (D * ) is enhanced to 1.12 × 10 12 Jones. As a demonstration, the photodetector can accurately measure human heart rate using the photoplethysmography method, highlighting its potential for biometric recognition and wearable devices. It is anticipated that this device design strategy can also be extended to other organic systems with narrower bandgaps.