Organic photodetectors can achieve narrowband photodetection within a single optoelectronic device. This comprehensive review summarizes and compares the different approaches, introduces their application fields, and outlines current challenges.

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Organic 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.

Extraction barriers are usually undesired in organic semiconductor devices since they lead to reduced device performance. In this work, we intentionally introduce an extraction barrier for holes, leading to nonlinear photoresponse. The effect is utilized in near-infrared (NIR) organic photodetectors (OPDs) to perform distance measurements, as delineated in the focus-induced photoresponse technique (FIP). The extraction barrier is introduced by inserting an anodic interlayer with deeper highest occupied molecular orbital (HOMO), compared to the donor material, into a well-performing OPD. With increasing irradiance, achieved by decreasing the illumination spot area on the OPD, a higher number of holes pile up at the anode, counteracting the built-in field and increasing charge-carrier recombination in the bulk. This intended nonlinear response of the photocurrent to the irradiance allows determining the distance between the OPD and the light source. We demonstrate fully vacuum-deposited organic NIR optical distance photodetectors with a detection area up to 256 mm 2 and detection wavelengths at 850 and 1060 nm. Such NIR OPDs have a high potential for precise, robust, low-cost, and simple optical distance measurement setups.