Hole injection engineering with MoO3 interlayer in organic light-emitting diode revealed by impedance spectroscopy

Inserting MoO3 interlayer between the indium–tin oxide anode and the most widely used hole transport layer of N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl) benzidine for engineering hole injection in organic light-emitting diode (OLED) is systematically investigated by using impedance spectroscopy. Based on the impedance versus frequency, phase versus frequency, and capacitance versus voltage characteristics, the suitable thickness of MoO3 interlayer is proven to be less than 30 nm. The suitable thickness of MoO3 interlayer is further verified by analyzing OLED efficiency. Our investigation indicates that a rather wide range of thickness tolerance of MoO3 interlayer to great extent facilitates OLED fabrication in practical application.