Probing the localization of charge and the extent of disorder through electronic transport on Au nanoparticle–copper phthalocyanine multijunction networks

Precision control of charge transport can provide a solid basis for the design of materials with novel properties. We report on the bottom-up fabrication and study of the electronic properties of molecular multijunction networks comprising ultrafine gold nanoparticles (AuNPs) of diameter ∼1.4 nm, electronically linked by means of copper 3-diethylamino-1-propylsulfonamide sulfonic acid-substituted phthalocyanine (CuPcSu) molecules. When electrons flow through the nonlinked nanoparticle arrays, they experience onsite Coulomb repulsion and are strongly localized, with a localization length ξ = 0.7 nm. Under dynamic excitation the system functions as a single electron-transport regulator, undergoing Coulomb oscillations, whereas the introduction of CuPcSu molecules results in the formation of a network of multiple molecular/Au nanojunctions and conductance increases by five orders of magnitude. This switching behavior functions on reversible redox reactions and pushes carriers into a state of weaker localization. In this state, electrons spread over several junctions and all temperature-scaled current versus voltage curves, J/T1 + α versus eV/kT, collapse into one universal curve, characterizing the network and the extent of its disorder. Utilizing this property, we demonstrate the effect of interelectrode distance on the conduction nodes' topological disorder. The system consists a promising candidate for Au NPs-based thin films with tunable properties wherever solution-based fabrication methods, such as injection printing, are envisioned.