Photodetectors based on chlorophyll for visible image sensing and near-infrared moving detection with bidirectional...

Photodetectors, with high sensitivity and broad spectral response, drive the advancements in optical imaging technology. In this work, utilizing the absorption differences of chlorophyll-a derivative (Chl) and [6,6]-phenyl-C₆₁-butyric acid methyl ester, two distinct structures of multifunctional organic photodetectors (OPDs) are fabricated, namely, bulk heterojunction (BHJ) and quasiplanar heterojunction (Q-PHJ). Chl, by modulating its doping concentration, served as both an active layer and an electron trap, enabling the BHJ OPD to exhibit a photomultiplication effect, and allowing the Q-PHJ OPD to achieve improved response speed (0.12/0.13 micros) and specific detectivity (2.20 × 10¹³ Jones). In addition, the visible image-sensing function has been demonstrated in the OPD arrays. Based on the bidirectional current response behavior of Q-PHJ OPD under bias voltage regulation, the moving detection function is implemented by combining it with background subtraction, extracting the moving objects from the image stream.