Macroscopic and Microscopic Charge Transport in Thin Films of Solution-Synthesized Graphene Nanoribbons

Graphene Nanoribbons (GNRs) are quasi-one-dimensional nanomaterials with unique optical and electronic properties that depend on their width and edge type. Bottom-up synthesis routes for GNRs offer precise control over these properties and even length but usually yield nanoribbons that also contain some structural defects such as missing phenyl rings or unclosed bonds in an otherwise perfect sp²-lattice. Theoretical and experimental studies on on-surface synthesized GNRs have shown that these defects alter the electronic structure of the GNRs. We have recently demonstrated that dispersions of solution-synthesized 9-aGNRs can be subjected to liquid cascade centrifugation to separate defective from pristine GNRs [ACS Nano 2023, 17, 21771] as proven by absorption, photoluminescence and Raman spectroscopy. Defective GNRs showed absorption and emission peaks at higher energies compared to the pristine GNRs, which was also corroborated by time-dependent density-functional theory (TDDFT) calculations.<br/><br/>So far only few examples of efficient charge transport in devices with thin films of GNRs have been reported. In addition to the required hopping between the individual nanoribbons, defects in the GNR lattice are predicted to significantly impair charge transport. Here, we investigate the impact of such defects on charge transport in thin films of 9-aGNRs and present a simple method to quantify and control the defect density in dense GNR films. We evaluate the macroscopic charge transport in electrochemically doped GNR films using electrolyte-gated transistors and in chemically doped GNR films by 4-point-probe conductivity measurements. We further examine the microscopic charge transport in GNRs depending on defect density by dark microwave conductivity measurements. The combination of these measurements enables us to correlate the defect density of GNRs with their optical and electronic properties.