(Invited) Measurement of the Energy-Band Relations of Stabilized Si Photoanodes Using Operando Ambient Pressure X-ray Photoelectron Spectroscopy

Amorphous TiO₂ coatings can stabilize semiconductor photoanodes such as Si, GaAs, and GaP that are otherwise unstable in aqueous media ^1-3. We employ Ambient Pressure Photoelectron Spectroscopy ^4,5 and standard X-Ray Photoelectron Spectroscopy to analyze light-absorber/protection-layer/catalyst stacks. The photoelectrochemistry coupled with AP-PES investigations have been performed at the Advanced Light Source, Berkeley at Beamline 9.3.1.

We show that the holographic information contained in the shape and width of core level peaks allows for determination of the electrostatic potential of semiconductor junctions by X-Ray photoelectron spectroscopy. Results for transition metal oxide protected light absorbers for photoelectrochemical energy conversion are shown. Energy band alignments at the light absorber/protection layer interface and for light-absorber/protection-layer/catalyst stacks with and without contact with aqueous electrolytes are investigated; evaluations with respect to semiconductor band bending and interfacial dipole shifts are presented.

1. S. Hu et al., Science, 344, 1005–1009 (2014).

2. M. F. Lichterman et al., Energy Environ. Sci., 7, 3334–3337 (2014).

3. H. J. Lewerenz, in Photoelectrochemical Materials and Energy Conversion Processes, R. C. Alkire, D. M. Kolb, J. Lipkowski, and P. N. Ross, Editors, vol. 12, p. 61–181, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany (2010).

4. S. Axnanda et al., Meet. Abstr., MA2013-02, 921–921 (2013).

5. S. Axnanda et al., (2014), submitted.