Ultrafast transient absorption spectroscopy of inkjet-printed graphene and aerosol gel graphene films : effect of oxygen and morphology on carrier relaxation dynamics

The tunable electronic properties of nanostructured graphene make it one of the most sought alternatives to metals for novel technological applications. In particular, the ability to prepare inks out of these nanostructures allows for printable and thus scalable graphene-based electronics. Here, we investigate the electronic properties of novel inkjet-printed aerosol gel graphene (AG) films and compare them to those of inkjet-printed graphene (G) films. More specifically, we report on the photoinduced carrier dynamics of these materials via ultrafast transient absorption spectroscopy. In comparison to graphene, AG films have a higher oxygen content as well as a complex 3D morphology. While G and AG both differ in composition and structure, the similitude in their carrier–optical phonon scatter rates (in 74–140 fs range) indicates a comparable lattice defect density. It is therefore not the number of defects but the type of defect that is electronically relevant. Indeed, in comparison to G films, which exhibit complete recovery of the transient signal, the AG films exhibit only partial recovery within our 400 ps experimental time window. The persisting signal is assigned to trapped electronic states. These long-lived electronic states are most probably due to the presence of oxygen rather than due to the films’ unique 3D morphology.