This talk will first discuss the parameters necessary for an optimal water-splitting device using a web based modeling program we developed (SolarFuelsModeling.com).¹ The results from this show an optimal a tandem device for water splitting needs photoabsorbers with band gaps of ~2.0 eV and 1.1 eV. After a short review on our work on small band gap Si photoelectrodes,^2-4 we will then discuss our combined computational and experimental approach to finding highly efficient large band gap photoabsorbers.⁵ Using computational modeling, we investigated ABS3 type sulfides and found 15 materials with a reasonable band gap, a direct band gap, low effective electron/hole mass and that are relatively defect tolerant. One of these proposed materials, LaYS₃ has already been tested and shows a direct band gap near 2 eV and a fluorescence spectra indicating no significant mid gap states as shown in the image below.

1. Seger, B.; Hansen, O.; Vesborg, P. C. K., A Flexible Web-Based Approach to Modeling Tandem Photocatalytic Devices. Solar RRL 2017, 1 (1), n/a-n/a.
2. Mei, B.; Permyakova, A. A.; Frydendal, R.; Bae, D.; Pedersen, T.; Malacrida, P.; Hansen, O.; Stephens, I. E. L.; Vesborg, P. C. K.; Seger, B.; Chorkendorff, I., Iron-Treated NiO as a Highly Transparent p-Type Protection Layer for Efficient Si-Based Photoanodes. Journal of Physical Chemistry Letters 2014, 5 (20), 3456-3461.
3. Mei, B.; Seger, B.; Pedersen, T.; Malizia, M.; Hansen, O.; Chorkendorff, I.; Vesborg, P. C. K., Protection of p(+)-n-Si Photoanodes by Sputter-Deposited Ir/IrOx Thin Films. Journal of Physical Chemistry Letters 2014, 5 (11), 1948-1952.
4. Seger, B.; Pedersen, T.; Laursen, A. B.; Vesborg, P. C. K.; Hansen, O.; Chorkendorff, I., Using TiO2 as a Conductive Protective Layer for Photocathodic H-2 Evolution. Journal of the American Chemical Society 2013, 135 (3), 1057-1064.
5. Kuhar, K.; Andrea, C.; Monish, P.; Kristian, S. T.; Brian, S.; Peter, V.; Ole, H.; Chorkendorff, I.; Karsten, W. J., Sulfide Perovskites for Solar Energy Conversion Applications: Computational Screening and Synthesis of the Selected Compound LaYS3. Energy & Environmental Science 2017, Accepted.