Impact of Defects on Solar Cell Performance in Low-Dimensional Selenium

Low-dimensional trigonal selenium (Se) was the first material to exhibit the photovoltaic effect and has recently experienced a renaissance in research interest as a candidate solar cell absorber, due to its desirable properties (suitable band gap, high earth abundance, low temperature processing), potential implementation in silicon tandem cells and <i>‘simple’ elemental chemistry</i>. Though cell efficiencies have improved much since its initial application in 1883, Se still lags behind leading technologies such as silicon and lead-halide perovskites, with the fundamental limitations (doping density, defect-mediated recombination, intrinsic Urbach tailing…) remaining unclear.<br/><br/>In this work, we use hybrid density functional theory to investigate the electronic properties, band alignment and defect chemistry of Se, in order to shed light on the key limiting factors for solar cells. We find the crystal dimensionality to dictate the energies of intrinsic defects (vacancies and interstitials) in this system and their impact on electronic properties. In doing so, we identify key deleterious impurities for performance and important considerations for the experimental fabrication of high-efficiency selenium solar cells, as well as establishing an outlook for the attainable performance of Se solar cells based off the fundamental intrinsic limitations.<br/> <br/><b>References:</b><br/>1 M. Zhu, G. Niu and J. Tang, <i>J. Mater. Chem. C</i>, 2019, <b>7</b>, 2199–2206.<br/>2 D. M. Chapin, C. S. Fuller and G. L. Pearson, <i>J. Appl. Phys.</i>, 1954, <b>25</b>, 676–677.<br/>3 A. Goetzberger, J. Luther and G. Willeke, <i>Sol. Energy Mater.</i>, 2002, 11.<br/>4 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, <i>Nat. Commun.</i>, 2017, <b>8</b>, 682.<br/>5 T. H. Youngman, R. Nielsen, A. Crovetto, B. Seger, O. Hansen, I. Chorkendorff and P. C. K. Vesborg, <i>Sol. RRL</i>, 2021, <b>5</b>, 2100111.<br/>6 S. R. Kavanagh, A. E. Samli, A. Walsh and D. O. Scanlon, Submitted