From Event: SPIE Optics + Photonics for Sustainable Energy, 2016
Silicon is a promising contender in the race for low-bandgap absorbers for use in a solar driven monolithic water splitting cell (PEC). However, given its role as the low-bandgap material the silicon must sit behind the corresponding high-bandgap material and as such, it will be exposed to (red) light from the dry back-side – not from the wet front side, where the electrochemistry takes place.[1,2] Depending on the configuration of the selective contacts (junctions) this may lead to compromises between high absorption and low recombination.[2,3] We discuss the tradeoffs and compare modeling results to measurements. Regardless of configuration, the wet surface of the silicon is prone to passivation or corrosion and must therefore be carefully protected in service in order to remain active. We demonstrate the use of TiO2 as an effective protection layer for both photoanodes and photocathodes in acid electrolyte  and NiCoOx for photoanodes in alkaline electrolyte. 
: B. Seger et alia, Energ. Environ. Sci., 7 (8), 2397-2413 (2014), DOI:10.1039/c4ee01335b
: D. Bae et alia, Energ. Environ. Sci., 8 (2), 650-660 (2015), DOI: 10.1039/c4ee03723e
: D. Bae et alia, submitted, (2016)
: B. Mei et alia, J. Phys. Chem. C., 119 (27), 15019-15027 (2015), DOI: 10.1021/acs.jpcc.5b04407
Peter C. Vesborg, Dowon Bae, Brian J. Seger, Ib Chorkendorff, Ole Hansen, Thomas Pedersen, Bastian Mei, and Rasmus Frydendal, "Protected, back-illuminated silicon photocathodes or photoanodes for water splitting tandem stacks
(Conference Presentation)," Proc. SPIE 9935, Solar Hydrogen and Nanotechnology XI, 99350E (Presented at SPIE Optics + Photonics for Sustainable Energy: August 30, 2016; Published: 3 November 2016); https://doi.org/10.1117/12.2238697.5167075342001.
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