Effects of charge injection barrier on the dark current of organic photodiodes

Abstract

In this work, we investigated the effect of charge injection barrier on the dark current density of organic photodetectors. The photosensitive layer of these photodetectors contains an electron-donating polymer PNTOD, and the derivatives of the widely used non-fullerene acceptor, namely ITIC, IT-2F and IT-4F. All devices showed similar absorption profiles and external quantum efficiencies, while different dark current density and thus specific detectivity. It is interesting to note that both electron and hole injection barriers of devices decreased with increased fluorine substituents in end groups of the non-fullerene acceptor ITIC. The electron injection barriers reduced from 1.37 eV for ITIC to 1.02 eV for IT-4F, and the corresponding hole injection barriers slightly dropped from 0.75 eV for ITIC to 0.57 eV for IT-4F, leading to an increased dark current at reversed bias. These findings verified the importance of rational energy level alignment of photosensitive materials for achieving high-performance organic photodetectors. • The effects of charge injection barrier on the dark current density of organic photodetectors were investigated. • OPDs based on ITIC derivatives showed similar photocurrent and responsivity, while obviously different dark current density and detectivity. • Increasing F-substituents of ITIC derivatives leads to decreased charge injection barrier and thus increased dark current density.