Stacked Dual‐Wavelength Near‐Infrared Organic Photodetectors

Abstract

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.

Highly Sensitive Narrowband Photomultiplication‐Type Organic Photodetectors Prepared by Transfer‐Printed Technology

“…The EQE at 660 nm of PMOPDs is about 760% under an applied voltage of −20 V. When the OFA layer thick ness is increased to 3.5 µm, the response peak is redshifted to 675 nm, and the corresponding EQE value is about 370% under an applied voltage of −20 V. To clarify the effect of OFA layer thickness on the performance of PMOPDs, optical distribu tion was investigated based on the device structure of ITO/ PEDOT:PSS/P3HT (3.5 µm)/P3HT:PC 71 BM (50 nm)/Al by employing the transfer matrix method. [33,34] The optical field distribution in the PMOPDs with 3.5 µm OFA layer and 50 nm PM layer is exhibited in Figure 3a. It is obvious that the incident photon with a wavelength of <670 nm can be completely harvested in the 3.5 µm thick OFA layer.…”

Narrowband organic photodetectors – towards miniaturized, spectroscopic sensing

“…Single-wavelength mode Physics of microcavities. In general, the intrinsic absorption coefficient (a) at peak wavelength of typical photo-absorbing materials is around 10 5 cm À1 , 82,85,194 which gives an absorption attenuation length of around 50 nm. Therefore, in normal organic electronic devices, such as OSCs, the needed photoabsorbing layer thicknesses are several tens to one hundred nanometers to achieve as high as possible absorption.…”

“…79 In 2017, tunable narrowband OPDs with BHJ embedded into Fabry-Pe ´rot microcavities 80 were accomplished, with single or dual wavelengths detection capabilities. 27,74,81,82 In 2020, Xing et al introduced self-filtering narrowband OPDs composed of a depletion layer, a donor and a thin acceptor layer, forming a planar heterojunction (PHJ). 83 Tunable red and NIR narrowband OPDs were achieved.…”

Wavelength‐Selective Organic Photodetectors

“…Figure shows D * values extracted from 43 papers reporting narrow‐band OPDs from the year 2012 onwards with an FWHM value of a maximum of 150 nm. [ 4,17–21,25,28,30–34,38–67 ] To get an overview of the current status of the field, it is instructive to plot D * as a function of peak EQE value, J d , and design wavelength. It is important to mention that not in all of these papers the noise currents have been directly measured and D * has often been calculated using , given by Equation (2).…”