Efficient noise suppression via controlling the optical cavity in near-infrared organic photoplethysmography sensors

Abstract

Herein, a high-sensitivity organic photodetector (OPD) that operates in the near-infrared region is proposed by controlling the micro-cavity effects. This strategy implements an extension of reactive wavelength in an organic-semiconductor-based active layer. Comprehensive analyses, including atomic force microscopy and energy-dispersive X-ray spectroscopy, confirm the enhanced surface morphology of the active layer despite elongated optical and electrical pathways. Moreover, electrochemical characterisation reveals an increase in shunt resistance and a reduction in defect density owing to increased vertical pathways. These improvements directly contribute to dark current suppression in the OPD, reducing it from 2.36 × 10⁻⁸ A cm⁻² under reference conditions to 7.07 × 10⁻¹⁰ A cm⁻² under optimal conditions. Consequently, both signal quality and the measurable signal range are significantly enhanced. The optimal performance point is red shifted from 760 to 830 nm via a customised spectral response that is more suitable for photoplethysmography (PPG) applications. The performance at 830 nm is as high as 3.35 × 10¹³ Jones. The PPG test proves the practical applicability of the proposed OPD, thus showcasing its potential in applications such as health monitoring and other relevant fields.