The performance of a photoelectrochemical solar cell (PEC) depends strongly on the electrochemical nature of the semiconductor/electrolyte junction. Operando ambient pressure X-ray photoelectron spectroscopy (OAP-XPS) investigation of solid/liquid junctions provides quantitative understanding of the energetic relations in PECs [1-3]. We demonstrate that OAP-XPS can be used to determine these relationships for solid/liquid systems. The OAP-XPS data can be analyzed to determine the relationship between the energy bands in a semiconductor electrode and the redox levels in the solution as well as directly analyze the energetics of the double layer at a metal-aqueous solution interface. From the response of the core level binding energy shifts and the broadening to variations in applied potential, we obtain the energetics of the solid/electrolyte interface. All major conditions for semiconductor-electrolyte contacts including accumulation, depletion, and Fermi-level pinning were observed, and the flat-band potential was determined. The data are compared to theoretical evaluations of the potential in the solid and electrolyte near the interface.

1. H.J. Lewerenz et al., Electrochimica Acta, 211, 711–719 2016

2. M. F. Lichterman et al., Journal of the Electrochemical Society, 163(2), H139–H146, 2016

3. M. F. Lichterman et al., Energy & Environmental Science, 8(8), 2409–2416, 2015