Polymer residues remaining after transfer of CVD graphene have detrimental effects for integration of graphene as transparent electrode in for instance OLEDs as they inhibit efficient charge transfer from graphene to the active layers in the device. Post-transfer annealing at elevated temperatures in high vacuum can remove polymer residues but may lead to an amorphisation of the graphene layer as indicated by Raman spectroscopy. There are currently no reports on how this amorphisation affects the electrical properties of the graphene layer. Here, we show that even though Raman spectroscopy suggests that the graphene quality seems to deteriorate after annealing, the sheet conductance of the sample increases. The increased sheet conductance measured by terahertz spectroscopy is more important from a device point of view compared to the lower quality of the graphene after annealing. 

Patrick Whelan is a PhD student at DTU Nanotech doing research in transfer and integration of graphene for OLED devices. He received his Master degree in Nanophysics and -materials from Aalborg University in 2013.