Photovoltaics as an Experimental Tool for Determining Frontier Orbital Energies and Photocatalytic Activity of Thiol Protected Gold Clusters

Abstract

Metal clusters are an emerging photonic material with a rapidly growing library of stable, atomically precise clusters recently reported. The growing interest in metal clusters, such as thiol-protected Au clusters, is due in part to interest in this new material for light harvesting, catalysis and electron transfer studies, and high efficiency photovoltaics (i.e., metal-cluster-sensitized solar cells (MCSSC) with long-term stability). Herein, we use cobalt redox couples as a tool to investigate the electronic properties (i.e., HOMO energy level) and the wavelength-dependent photocatalytic activities of glutathione protected gold clusters. To this purpose, we have synthesized a series of cobalt complexes with bipyridine and phenanthroline derivatives in order to study Au18(SR)14 and Au25(SR)18 sensitized solar cells. Using cobalt complex mediators as an alternative to the conventional high performance I–/I3– electrolyte, long-term performance of MCSSC is achieved. Furthermore, these one-electron redox mediators conclusively demonstrate the unique optical activity of clusters, with excitation-wavelength-dependent photocatalytic activity.