To further assess the potential of Cu 2 SiSe 3 for solar cell operation, an understanding of its defect chemistry is required. High concentrations of deep defects limit the performance of most emerging photovoltaic absorbers. These deep states enable the non-radiative recombination of charge carriers, reducing device efficiencies. Formation energies for all intrinsic defects of Cu 2 SiSe 3 were calculated and the transition level diagrams under the most Cu-poor and Cu-rich conditions are shown in Figure . The chemical potential space for Cu 2 SiSe 3 is bound by seven intersections, with the most Cu-poor regions also being Si-poor, and the most Cu-rich being relatively Si-rich.