Reverse Dark Current in Organic Photodetectors: Generation Paths in Fullerene Based Devices

Abstract

AbstractOPDs have promising applications in low-cost imaging, health monitoring and near infrared sensing. Recent research on OPDs based on donor-acceptor systems has already resulted in narrow-band, flexible and biocompatible devices, with the best reaching photovoltaic external quantum efficiencies of almost 100%. However, the high noise spectral density \((S_{n})\) of these devices limits their specific detectivity to around \(\mathit{10}^{\mathit{13}}\) Jones in the visible and several orders of magnitude lower in the NIR, severely reducing the performance. Here, we show that the shot noise, proportional to the dark current \((J_{D})\), dominates \(S_{n}\), demanding a comprehensive understanding of \(J_{D}\). We demonstrate that, in addition to the intrinsic saturation current generated via charge-transfer (CT) states, \(J_{D}\) contains a major contribution from trap-assisted generated charges and decreases systematically with decreasing concentration of traps. By modeling \(J_{D}\) of several donor-acceptor systems, we reveal the interplay between traps and CT states as source of dark current and show that traps dominate the generation processes, thus being the main limiting factor of the OPDs detectivity. This chapter is adapted from work published in J. Kublitski, A. Hofacker, B. K. Boroujeni, J. Benduhn, V. C. Nikolis, C. Kaiser, D. Spoltore, H. Kleemann, A. Fischer, F. Ellinger, K. Vandewal, and K. Leo, “Reverse Dark Current in Organic Photodetectors and the Major Role of Traps as Source of Noise”, Nature Communications, vol. 12, p. 551, 2021 [1].