Cu₂SiSe₃—A Defect Tolerant, Earth Abundant Semiconductor with PV and Thermoelectric Applications

Low-cost, non-toxic and earth-abundant materials are a long-sought after target in the photovoltaics research community. Initially, chalcogenides were the frontrunners to replace Si as the next generation of thin film solar absorbers, however, the initial promise of CIGS and CZTS has since slowed considerably. In this presentation, I will outline our computational and experimental analysis of Cu₂SiSe₃, which was initially identified due to its simple ternary composition, and the favourable difference in charge and size between the cation species, potentially limiting antisite defects and cation disorder. We find it to have an ideal, direct bandgap of 1.52 eV and a maximum efficiency of 30% for a 1.5 μm-thick film at the radiative limit. Using hybrid density functional theory, the formation energies of all intrinsic defects are calculated, revealing the p-type copper vacancy as the dominant defect species, which forms a perturbed host state. Overall, defect concentrations are predicted to be low and have limited impact on non-radiative recombination, as a consequence of the p–d coupling and antibonding character at the valence band maxima.[1] We also present detailed experimental growth and characterisation investigations, and use cluster expansion methods to explore polymorphism in this system.<br/><br/>[1] A. T. Nicolson, S. R. Kavanagh, C. N. Savory, G. W. Watson and D. O. Scanlon, Cu₂SiSe₃ as a promising solar absorber: harnessing cation dissimilarity to avoid killer antisites, <i>Journal of Materials Chemistry A</i>, <b>11</b> 14833 (2023)