Deciphering the Redox-Controlled Stabilization Effect on Conduction Band Energies of Silicon Nanointerfaces Functionalized with N-Type Monolayers of Perylene Bisimides

Surface confinement of π-conjugated organic molecules on semiconducting silicon (Si) electrodes is a prevalent strategy to develop redox-active hybrid nanointerfaces for applications in microelectronics, spin filters, electrochemical sensors, and information technology. While conventional approaches to functionalize Si surfaces primarily exploit molecularly dissolved p-type (electron rich) units, leveraging π-aggregated n-type (electron poor) organic units to control the electronic structures and semiconducting properties of Si interfaces remains very elusive. This study deciphers a novel redox-controlled stabilization effect that is unique to Si surfaces functionalized with n-type monolayers of π-aggregated perylene bisimides (PBIs). For this type of n-type Si nanointerfaces, the cathodic reduction potential necessary for injecting negative charge carriers into the conduction band of the PBI monolayer is shown to be reversibly stabilized > 375 mV by varying the maximum anodic potential (MAP) that is applied during the anodic cycle (i.e., +0.5 or +1.5 V vs Ag/AgCl). Leveraging a set of PBI-based molecular systems, we show that the magnitude of such redox-controlled stabilization effect can be modulated by the structure-property relationships of the PBI π-aggregates that are employed to generate the n-type monolayers on Si surfaces. In contrast, such a redox-controlled stabilization effect is not evidenced for Si interfaces accessed from monolayers of molecularly dissolved PBI units as well as from Si precursors featuring a low density of anchoring moieties. Corroborated with DFT calculations that reveal a substantial structural reorganization in a model, partly p-doped PBI π-aggregate, the experimental results suggest that a MAP of +1.5 V vs Ag/AgCl engenders structural reorganization of the monolayers derived uniquely from PBI π-aggregates. It is proposed that conformational perturbations instigated at a high MAP (+1.5 V) leads to the formation of electronic states which further expediate electron injections. In essence, the results offer a proof-of-principle that transferring the structure-property relationships of n-type organic π-aggregates on Si electrodes is a powerful strategy to develop semiconducting nanointerfaces whose conduction band energies can be reversibly redox-controlled. This study may lay the foundation stone for developing a novel gamut of redox-switchable Si nanointerfaces for application in nonvolatile electronic memory devices.