Abstract
Organic photodetectors have promising applications in low-cost imaging, health monitoring and near-infrared sensing. 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%. However, the high noise spectral density of these devices limits their specific detectivity to around 1013 Jones in the visible and several orders of magnitude lower in the near-infrared, severely reducing performance. 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. 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. 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.
Highlights
Organic photodetectors have promising applications in low-cost imaging, health monitoring and near-infrared sensing
The specific detectivity is proportional to the external photovoltaic quantum efficiency (EQE) and inversely proportional to spectral density (Sn): pffiffiffi
If Sn is assumed to be dominated by the shot noise and is calculated in the radiative limit, D*can be improved by six orders of magnitude, considering the real EQE
Summary
Organic photodetectors have promising applications in low-cost imaging, health monitoring and near-infrared sensing. 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, being the main limiting factor of organic photodetectors detectivity. PDs for the visible and near-infrared spectral region are mainly based on silicon (Si) and indium gallium arsenide (InGaAs) alloys While their performance is outstanding, devices and imagers are expensive and inflexible. The measured JD is orders of magnitude higher than the ideal, thermally generated dark current, J0, calculated within the radiative limit[14] This discrepancy is commonly observed in OPDs and is the main limiting factor for achieving higher detectivities. ECT determines the thermal lower limit of JD to seek for and provides a metric for judging how far JD is from this fundamental limit
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