Reverse dark current in organic photodetectors and the major role of traps as source of noise

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.

Miniaturized VIS‐NIR Spectrometers Based on Narrowband and Tunable Transmission Cavity Organic Photodetectors with Ultrahigh Specific Detectivity above 1014 Jones

“…J d scales with the total trap density and the shot-like behavior can be attributed to the detrapping of charge carriers. [35,36] The relatively stable EQE values with increasing reverse bias suggest less space for further improvement of the photoresponse by promoting charge collection. This emphasizes that the J d characteristics rather than the photoresponse performance establish the limit for the detection.…”

Mid-gap Trap State Mediated Dark Current in Organic Photodiodes

“…18 Recently, the effect of mid-gap trap states has also been observed in the sub-gap EQE 19 directly and by impedance spectroscopy. 20 In this work, we provide evidence that the dark saturation current in organic photodiodes is dominated by recombination via mid-gap trap states. To minimize the influence of the shunt, we use narrow-gap BHJs with a relatively high 0 ( , ) such that at low reverse bias 0 > | shunt |.…”

Mid-gap trap state mediated dark current in organic photodiodes

“…18 Recently, the effect of mid-gap trap states has also been observed in the sub-gap EQE 19 directly and by impedance spectroscopy. 20 In this work, we provide evidence that the dark saturation current in organic photodiodes is dominated by recombination via mid-gap trap states. defining an active area of 4 mm².…”