A variety of copper chalcogenides with suitable bandgaps for visible light absorption have emerged from these coarse screening studies, including CuSb(S,Se) 2 , Cu 2 (Si,Sn)Se 3 and LiCuS. To further reduce the number of candidate materials, we can learn from the failures of CZTS to employ several design principles to guide the search for a defect tolerant, diamond-like photovoltaic absorber, which could be integrated into current device architectures. By selecting cations with larger differences in charge and ionic radii, the prevalence of cation disorder and detrimental antisite defects could be reduced. To this end, we computationally investigated Cu 2 SiSe 3 (Si IV (r = 0.26 Å) and Cu I (r = 0.6 Å)), which had also been identified to have an ideal bandgap from screening studies using the semi-local mBJ+U DFT functional. We calculated the electronic and optical properties of Cu 2 SiSe 3 using both hybrid DFT and Green's function (GW ) methods, including the radiative efficiency limits and electronic band alignment. Given that defect-induced carrier recombination is the dominant limiting factor for power-conversion efficiencies in emerging PV absorbers, an understanding of the intrinsic defect thermodynamics is crucial for establishing an accurate outlook on the potential PV performance. Defect calculations were therefore performed using hybrid DFT to gain a complete picture of the intrinsic defect chemistry. In doing so, we predict Cu 2 SiSe 3 to contain low concentrations of deleterious defects. We expect our results will inspire further investigations into Cu 2 SiSe 3 for photovoltaic applications.