Inkjet printed graphene as an interconnect for optoelectronic devices

A comparative study of inkjet-printed graphene films (IPGFs) with mechanically exfoliated, highly crystalline graphene platelets have been conducted. Inkjet-printed graphene films were obtained using liquid-phase exfoliation of bulk graphite, while crystalline, residue-free graphene was obtained from highly-oriented-pyrolytic-graphite (HOPG) using mechanical exfoliation through a viscoelastic transfer process. Optical absorption spectroscopy was used to infer the density of platelets in the graphene-based ink dispersion. Temperature-dependent Raman spectroscopy revealed the presence of the defect D-band peak in the IPGFs, which was not observed in the HOPG-based samples at room temperature, confirming the higher crystalline quality of the latter. Full-width-half-maximum (FWHM) of the G-band was measured to be similar to 26.4cm(-1) for IPGFs compared to similar to 18.6cm(-1) for HOPG-based samples. Moreover, the D-band intensity decreased as temperature increased up to 600 degrees C for IPGFs, suggesting the possibility of annealing effects that may arise at these temperatures to reduce defect densities. In both HOPG-based samples and IPGF patterns, the G-band and G '-band red-shifted with increasing temperature which can be attributed to elongation of the C-C bond due to thermal expansion, resulting in the anharmonic coupling of the phonon modes. Moreover, a power study demonstrated the IPGFs even with printing passes as low as 10 passes, dissipate similar to 1.03 mW of power at 1V, which was similar to the power dissipated in the HOPG samples (similar to 1.05 mW at 1V) suggesting good adherence of graphene platelets and high conductivity in IPGFs, which suggests that the inks are favorable for use in interconnects for device platforms in printed electronics. A natural follow-on from this work, was the use of the conductive graphene inks as an interconnect in devices, specifically WS2-based photodetectors, where prototype devices were fabricated and characterized that are also discussed here.