Factors governing photo- and dark currents in lateral organic photo-detectors

Abstract

We study the factors governing the dark and photo currents in lateral organic photodetectors (OPD). The dark current is found to be strongly limited by space charge limited conduction (SCLC) across a highly depleted gap and arises mostly from transient capacitive currents due to the charge accumulation in the organic layers near the contacts. Similarly, the photocurrent is found to be strongly limited by the collection of photogenerated carriers at the contacts, which limits the sensitivity of lateral OPDs. Furthermore, evidence of the contribution of some photons falling outside of the gap area are reported and have to be taken into account when one wants to conduct accurate external quantum efficiency estimates of lateral OPDs. Finally, it is found that the dark current is significantly increased after the device is exposed to light, likely to be due to the filling of charge traps by photogenerated carriers, while the photocurrent remains unchanged, leading to a decrease in the overall sensitivity of the device upon repeated exposure to light. The results shed the light on the performance limitations in lateral OPDs.