The orbital-decomposed electronic density of states in Figure shows that the valence band is made up of Cu d and Se p states, with the conduction band predominantly Se p and Si s. Cu 2 SiSe 3 has an antibonding valence band maximum (VBM), illustrated by the Crystal Orbital Hamiltonian Population analysis shown in Figure . This is typical of materials with occupied (semi-)valence cation orbitals (e.g. d 10 Cu 1+ ), and is associated with the formation of shallow acceptor defects. The highly dispersive conduction band results in low electron effective masses (<0.20 m 0 ) indicating highly mobile carriers, beneficial for the extraction of minority charge carriers in a p-type absorber. The hole masses have much greater anisotropy, with an effective mass of 1.87 m 0 from Γ to V, but 0.18 m 0 Γ to A -revealing fast transport for both carriers in Cu 2 SiSe 3 . A full breakdown of the calculated effective masses is given in Table . Two metrics for predicting the maximum photovoltaic efficiency were calculated; the spectroscopic limited maximum efficiency and the method of Blank et al., which take into account the bandgap and the absorption coefficient of a material. Using these metrics, Cu 2 SiSe 3 reaches a maximum efficiency of 30% at a thickness of 1.5µm, with a Lambertian structured surface increasing efficiency at thinner film thicknesses (Figure ).