Secondary functionalization of passivated Si(111) : pathways to stable photoelectrode systems

Silicon surfaces functionalized with electrochemically-active metal complexes and clusters are an important family of functional interfaces. These systems have shown promise for solar energy conversion and storage, molecular electronics, and biological and chemical sensing applications. However, surface stability is a limiting factor that has persistently challenged the broad implementation and in-depth study of photoelectrochemistry at chemically-modified Si surfaces. The work presented herein demonstrates that secondary functionalization of passivated Si(111) surfaces is a versatile means to generate stable Si-based photoelectrodes comprised of surface-tethered metal-containing redox species. Organic mixed monolayers and metal oxide overlayers were used as platforms for the immobilization of a macro-chelated Ni(II)-bis-diphosphine complex and heteropolytungstate clusters on oxide-resistant Si(111). Rigorous physical and (photo)electrochemical analyses were used to probe analyte surface coverages, asses interfacial electron transfer kinetics, and indicate the extent of band bending in each sample. Thus, the high stabilities of these samples’ surfaces were revealed, which enabled deconvolution of kinetic and thermodynamic structure-function relationships that govern photoelectrochemical outcomes of these systems. These studies revealed the importance of band-edge modulation as a primary design consideration in the development of optimized chemically-modified photoelectrodes.Chemistr