Dark current reduction of small molecule organic photodetectors by controlling gap states of molybdenum oxide buffer layers

The gap states of the molybdenum-oxide (MoO_x) hole-extraction layer (HEL) in an organic photodetector (OPD) device, which originate from oxygen-vacancy defects, are controlled by appropriate plasma treatments on the MoOx layer. The density of MoOx gap states, investigated using X-ray photoelectron spectroscopy (XPS), is enhanced and depressed with Ar-and O2-plasma treatments, respectively. The dark current of an OPD with a MoO_x HEL is considerably reduced by controlling the MoO_x gap states using the plasma-treatment method. The mechanism of dark-current reduction may be interpreted by reduced gap states and by a suitable energy level bending and alignment.