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.

Detection of electromagnetic signals for applications such as health, product quality monitoring or astronomy requires highly responsive and wavelength selective devices. Photomultiplication-type organic photodetectors have been shown to achieve high quantum efficiencies mainly in the visible range. Much less research has been focused on realizing near-infrared narrowband devices. Here, we demonstrate fully vacuum-processed narrow- and broadband photomultiplication-type organic photodetectors. Devices are based on enhanced hole injection leading to a maximum external quantum efficiency of almost 2000% at −10 V for the broadband device. The photomultiplicative effect is also observed in the charge-transfer state absorption region. By making use of an optical cavity device architecture, we enhance the charge-transfer response and demonstrate a wavelength tunable narrowband photomultiplication-type organic photodetector with external quantum efficiencies superior to those of pin-devices. The presented concept can further improve the performance of photodetectors based on the absorption of charge-transfer states, which were so far limited by the low external quantum efficiency provided by these devices.

Spectroscopic photodetection plays a key role in many emerging applications such as context‐aware optical sensing, wearable biometric monitoring, and biomedical imaging. Photodetectors based on organic semiconductors open many new possibilities in this field. However, ease of processing, tailorable optoelectronic properties, and sensitivity for faint light are still significant challenges. Here, the authors report a novel concept for a tunable spectral detector by combining an innovative transmission cavity structure with organic absorbers to yield narrowband organic photodetection in the wavelength range of 400–1100 nm, fabricated in a full‐vacuum process. Benefiting from this strategy, one of the best performed narrowband organic photodetectors is achieved with a finely wavelength‐selective photoresponse (full‐width‐at‐half‐maximum of ≈40 nm), ultrahigh specific detectivity above 1014 Jones, the maximum response speed of 555 kHz, and a large dynamic range up to 168 dB. Particularly, an array of transmission cavity organic photodetectors is monolithically integrated on a small substrate to showcase a miniaturized spectrometer application, and a true proof‐of‐concept transmission spectrum measurement is successfully demonstrated. The excellent performance, the simple device fabrication as well as the possibility of high integration of this new concept challenge state‐of‐the‐art low‐noise silicon photodetectors and will mature the spectroscopic photodetection into technological realities.

Sequentially solution-processed polymer photodetectors (SSP PPDs) based on poly(3-hexylthiophene-2,5-diyl) (P3HT)/[6,6]-phenyl C-butyric acid methyl ester (PCBM) are fabricated by depositing the top layers of PCBM from an appropriate cosolvent of 2-chlorophenol (2-CP)/o-dichlorobenzene (ODCB) onto the predeposited bottom layers of P3HT. By adjusting the ratio of 2-CP/ODCB in the top PCBM layers, the resulting SSP PPD shows a decreased dark current and an increased photocurrent, leading to a maximum detectivity of 1.23 × 10 Jones at a wavelength of 550 nm. This value is 5.3-fold higher than that of the conventional bulk heterojunction PPD. Morphology studies reveal that the PCBM partially penetrates the predeposited P3HT layer during the spin-coating process, resulting in an optimal three-phase morphology with one well-mixed interdiffusion P3HT/PCBM phase in the middle of the bulk and two pure phases of P3HT and PCBM at the two electrode sides. We show that the pure phases form high Schottky barriers (>2.0 eV) at the active layer/electrodes interface and efficiently block unfavorable reverse charge carrier injection by significantly decreasing the dark current. The interdiffussion phase enlarges the donor-acceptor interfacial area leading to a large photocurrent. We also reveal that the improved performance of SSP PPDs is also due to the enhanced optical absorption, improved P3HT crystallinity, increased charge carrier mobilities, and suppressed bimolecular recombination.

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.