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

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-C 61 -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 μs) and specific detectivity (2.20 × 10 13  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.