(Invited) Selenium as a Top-Cell Absorber Candidate for Tandem Photoelectrochemical Stacks

The ideal high-bandgap partner for a tandem solar absorber using c-Si as the low-bandgap bottom cell must have a bandgap of around 1.9 eV and excellent optoelectronic properties. Selenium, perhaps the very first material to be studied for its photovoltaic properties, is emerging as an interesting candidate for this application. Indeed Se has a bandgap of around 1.95 eV [1] and a steep increase in absorption above this photon energy. Todorov et al showed [2] in 2017 that single-junction Se solar cells could reach 6.5% efficiency using a new cell architecture with a very thin absorber layer. Recently we have increased the OCV to a new record of 991 mV [2]. Simultaneously, we are also starting to identify the main shortfalls of state-of-the-art Se films which so far have prevented Se-cells from approaching their theoretical potential OCV, which is of course much higher than 991 mV. The talk will introduce Se as a solar absorber and discuss we know about its properties and use in solar devices such as PEC stacks. [1] T. K. Todorov, S. Singh, D. M. Bishop, O. Gunawan, Y. S. Lee, T. S. Gershon, K. W. Brew, P. D. Antunez and R. Haight, Nature Communications, 2017, 8, 682 [2] R. Nielsen, T. Youngman, H. Moustafa, S. Levcenco, H. Hempel, A. Crovetto, T. Olsen, O. Hansen, I. Chorkendorff, T. Unold, P. C. K. Vesborg, (in preparation), 2022