In an ideal diode, in addition to the diffusion current, the dark saturation current ( J 0) comprises a thermally activated component as a result of thermal generation of charges over the gap of the material 12. While the above-mentioned J D suppression approaches lead to an improved OPD performance, a comprehensive understanding of the intrinsic and extrinsic sources of dark current is still missing, which would provide insights for future device optimization using improved materials or architectures. Most frequently used approaches are charge selective layers 4, 5, contact alignment 6, 7, prevention of shunt paths via layer thickness increase 8, and interlayers to smoothen the bottom contact 9, 10, as well as charge transport layer structuring 11. Among the many sources of noise, the shot noise, proportional to the dark current, has been suggested to play a major role 2, especially because OPDs usually operate in reverse bias voltages, where the measured reverse dark current ( J D) strongly deviates from its ideal value.ĭark current suppression in organic diodes has been the subject of several reports in the literature 3. On the other hand, organic photodetectors (OPDs) can be significantly cheaper, but these devices still suffer from a high S n, resulting in rather low detectivities. While their performance is outstanding, devices and imagers are expensive and inflexible. Currently, PDs for the visible and near-infrared spectral region are mainly based on silicon (Si) and indium gallium arsenide (InGaAs) alloys. ![]() Besides a high responsivity, a low-noise spectral density ( S n), resulting in a high specific detectivity ( D *), is a key requirement. Light sensing and imaging 1 are important technological fields and create high demand for photodetectors (PDs). By modeling the dark current of several donor–acceptor systems, we reveal the interplay between traps and charge-transfer states as source of dark current and show that traps dominate the generation processes, thus being the main limiting factor of organic photodetectors detectivity. ![]() We demonstrate that, in addition to the intrinsic saturation current generated via charge-transfer states, dark current contains a major contribution from trap-assisted generated charges and decreases systematically with decreasing concentration of traps. Here, we show that the shot noise, proportional to the dark current, dominates the noise spectral density, demanding a comprehensive understanding of the dark current. However, the high noise spectral density of these devices limits their specific detectivity to around 10 13 Jones in the visible and several orders of magnitude lower in the near-infrared, severely reducing performance. Recent research on organic photodetectors based on donor–acceptor systems has resulted in narrow-band, flexible and biocompatible devices, of which the best reach external photovoltaic quantum efficiencies approaching 100%. Organic photodetectors have promising applications in low-cost imaging, health monitoring and near-infrared sensing. Is low dark current important for my imaging? Whether a given dark current value will contribute significantly to your images’ signal-to-noise ratio and image quality depends entirely upon your imaging scenario.įor high-light imaging scenarios with thousands of photons per pixel after a camera exposure, dark current is highly unlikely to be significant in image quality unless exposure ti mes are very long (tens of seconds to minutes) such as in astronomy applications. At the end of the exposure, all charges are measured cleared from the pixel ready for the next exposure.ĭark current noise is temperature dependent, but it is also highly dependent upon the camera sensor’s design and architecture and camera electronics, so can vary greatly from camera to camera at the same sensor temperature. However, the precise number of electrons is random, leading to the contribution of dark current noise. During the exposure of an image, these thermal electrons can build up, contributing to a background dark current signal. It is impossible to distinguish between these ‘thermal’ electrons and electrons that have arisen through the successful detection of a photon. ![]() All atoms experience thermal vibrational motion, and occasionally an electron can ‘jump’ out of the camera sensor’s substrate into a the pixel well where detected photoelectrons are stored. Dark current noise is caused by the thermal motion of electrons within the camera sensor.
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