Organic Cavity Photodetectors Based on Nanometer-Thick Active Layers for Tunable Monochromatic Spectral Response

Application of spectroscopic photodetecting technologies in future innovations such as wearable or integrated electronics will require miniaturized spectrometers. This can be achieved by using an array of small-area, wavelength-selective photodetectors. Here, filterless narrowband photodetectors based on a novel device concept are demonstrated. The narrowband photoresponse is realized by utilizing nanometer-thick 2,2-((3,4-dimethyl-[2,2:5,2:5,2:5,2-quinquethiophene]-5,5-diyl)­bis (methanylylidene))-dimalononitrile (DCV5T-Me):C60 photoactive layers (3–6 nm) in a Fabry–Perot cavity. By varying the cavity thickness, achieved by adjusting the transport layer thicknesses, we realize continuously tunable detection wavelengths, spanning the entire visible region (400–700 nm). Most importantly, because the active layer is only nanometer-thick, position of the active layer can be adjusted within the cavity. Thus, with an optimized position of the active layer, the photodetectors exhibit an overtone free, monochromatic spectral response with a full-width-at-half-maximum value of 25 nm and an external quantum efficiency over 50%. Although the absorber layers were kept thin, we realize peak specific detectivities over 1012 Jones, which is comparable to that of the most efficient narrowband organic photodetectors lacking spectral tunability over a broad wavelength range