The capability of detecting visible and near infrared light within a narrow wavelength range is in high demand for numerous emerging application areas, including wearable electronics, the Internet of Things, computer vision, artificial vision and biosensing. Organic and perovskite semiconductors possess a set of properties that make them particularly suitable for narrowband photodetection. This has led to rising interest in their use towards such functionality, and has driven remarkable

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... in recent years. Through a comparative analysis across an extensive body of literature, this review provides an up-to-date assessment of this rapidly growing research area. The transversal approach adopted here focuses on the identification of: (a) the unifying aspects underlying organic and perovskite narrowband photodetection in the visible and in the near infrared range; and (b) the trends relevant to photoconversion efficiency and spectral width in relation to material, device and processing strategies. A cross-sectional view of organic and perovskite narrowband photodetection is thus delineated, giving fresh insight into the status and prospects of this research area. photodetector stack and that act as transmission gratings [14] ; the use of patterned metal structures that exploit plasmonic effects [15] [16] [17] [18] . Organic semiconductors and metal-halide perovskite semiconductors are particularly well-suited for narrowband photodetection in the visible and the near infrared range. First and foremost, their attractiveness arises from the facile tunability of their absorption properties. On one hand, the absorption spectra of organic semiconductors can be tuned nearly at will via molecular design. This enables compounds with either broadband or narrowband absorption, their onsets covering the whole of the visible and the NIR range. On the other hand, while possessing a generally broadband character, metal-halide perovskite semiconductors enable facile tuning of their absorption onset through compositional engineering. In addition to their attractive spectral tunability, organic and perovskite semiconductors typically feature strong absorption (absorption coefficient α up to ≈10 5 cm −1 ) and high photoconversion efficiency. This allows photodetection to be realised within photoactive layers with a typical thickness of around 100-200 nm, which is ideal for high-resolution imaging applications (cf. thickness in the micrometre range is needed in conventional silicon technology). Finally, both organic and perovskite semiconductors can be deposited at low temperatures (<100°C) and via solution-based methods (e.g., printing and coating). Therefore, they are particularly attractive for large-area and potentially low-cost manufacturing on flexible plastic substrates, thus pointing to the development of narrowband photodetectors with new functionalities and form factors. Recent years have witnessed a surge in narrowband photodetector research relying on organic and perovskite semiconductors. Highly efficient and inherently narrowband photodetectors with spectral widths of about 100 nm have become possible. Additionally, effective strategies have been developed so as to harness broadband organics and perovskites in narrowband photodetectors with spectral widths down to 10 nm. This review is motivated by the need for an up-to-date assessment of this rapidly growing research area, particularly with respect to photoconversion efficiency and spectral width, which are central to narrowband functionality. While recent reviews on organic and perovskite narrowband photodetection have captured a broad view of the area [19] [20] [21] , the present article pursues a focused approach aiming at the identification of the general trends associated with photoconversion efficiency and spectral width. Indeed, the growing body of literature poses R defined as: 3 J. Phys.: Mater. 2 (2019) 042001 V Pecunia