Barrierless hole injection through sub-bandgap occupied states in organic light emitting diodes using substoichiometric MoO_x anode interfacial layer

摘要

In this letter, highly efficient hole injection was demonstrated in hole only devices based on organic semiconductors with different highest occupied molecular orbital level and transport properties. The barrierless hole injection was achieved by using a substoichiometric MoO_x thin film (consisting of 65% Mo~(+6) and 35% Mo~(+5)) as a higly effective anode interfacial layer. The current in these devices was found to be space charge limited, achieved due to the formation of highly efficient anode ohmic contact via the excellent band alignment through occupied gap states at the ITO/MoO_x and MoO_x/organic semiconductor modified interface. Quite remarkably, the efficiency of hole injection was found to be almost independent of the MoO_x thickness, which is indicative of perfect band alignment at the anode interface.