Insight into trap state dynamics for exploiting current multiplication in organic photodetectors

Trap-induced current multiplication has received tremendous attention in organic photodetectors because it is not required for a pre-amplifier circuit to read weak photocurrent signals. However, a plausible correlation between energy-distinguishable trap states and device performance has not been established for guiding the device design, a task that remains a significant challenge. Here, we propose an ingenious strategy to demonstrate current multiplication by engineering an ultrathin fullerene (C-60) film as hole trap or barrier layer, which illustrates trap-state dynamics through systematical investigations on device current fluctuations in darkness and illumination conditions. The comparison of trap-dependent performances between experimental and control devices clearly shows that the traps play a critical role in generating the multiplication effect. And shallow trap states are estimated to be more favorable for improving the device restorability. Thus, we anticipate that trap engineering, by selectively passivating deep traps whilst retaining shallow ones, will be a fruitful approach for further research, leading to high-performance photodetectors with superior current multiplication and temporal response. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim