Applied Surface Science, Vol.397, 144-151, 2017
Hole injection enhancement in organic light emitting devices using plasma treated graphene oxide
The hole injection layer (HIL) with high work function (WF) is desirable to reduce the injection barrier between anode and hole transport layer in organic light emitting devices (OLED). Here, we report a novel approach to tune the WF of graphene oxide (GO) using oxygen and hydrogen plasma treatment and its hole injection properties in OLEDs. The mild exposure of oxygen plasma on GO (O-2-GO) significantly reduces the injection barrier by increasing the WF of anode (4.98 eV) through expansion of C-O bonds. In contrast, the hole injection barrier was drastically increased for hydrogen plasma treated GO (H-2-GO) layers as the WF is lowered by the contraction of C-O bond. By employing active O-2-GO as HIL in OLEDs found to exhibit superior current efficiency of 4.2 cd/A as compared to 3.3 cd/A for pristine GO. Further, the high injection efficiency of O-2-GO infused hole only device can be attributed to the improved energy level matching. Ultraviolet and X-ray photoelectron spectroscopy were used to correlate the WF of HIL infused anode towards the enhanced performance of OLEDs with their capricious content of C-O in GO matrix. (C) 2016 Elsevier B.V. All rights reserved.