Stacked Dual‐Wavelength Near‐Infrared Organic Photodetectors

Abstract

AbstractOrganic near‐infrared (NIR) detectors have potential applications in biomedicine, agriculture, and manufacturing industries to identify and quantify materials contactless, in real time and at a low cost. Recently, tunable narrow‐band NIR sensors based on charge‐transfer state absorption of bulk‐heterojunctions embedded into Fabry‐Pérot micro‐cavities have been demonstrated. In this work, this type of sensor is further miniaturized by stacking two sub‐cavities on top of each other. The resulting three‐terminal device detects and distinguishes photons at two specific wavelengths. By varying the thickness of each sub‐cavity, the detection ranges of the two sub‐sensors are tuned independently between 790 and 1180, and 1020 and 1435 nm, respectively, with full‐width‐at‐half‐maxima ranging between 35 and 61 nm. Transfer matrix modeling is employed to select and optimize device architectures with a suppressed cross‐talk in the coupled resonator system formed by the sub‐cavities, and thus to allow for two distinct resonances. These stacked photodetectors pave the way for highly integrated, bi‐signal spectroscopy tunable over a broad NIR range. To demonstrate the application potential, the stacked dual sensor is used to determine the ethanol concentration in a water solution.