Computational design of p-type transparent conductors for photovoltaic applications

Ternary oxides are particularly attractive for applications ranging from transparent electronics to spintronics to photoelectrocatalysis, yet difficulties in achieving p-type conductivities have hindered progress in these fields. A common means of searching for ternary oxides has been to sample the triangular phase space and determine whether the most favorable structures are thermodynamically stable. We believe, however, that computational techniques must be improved to enable accurate property predictions and facilitate the search for these new materials. As an example, we propose that late transition metal zinc oxide spinel compounds, as identified by the Materials Project, may exhibit p-type behavior and good optical properties for use as transparent conducting oxides. We use density functional theory calculations and the Boltzmann transport equation to calculate electrical transport and optical properties of the candidate materials. We employ several improvements to the theory, namely: 1. Hybrid density functionals to account for the incorrect treatment of electron exchange in DFT, and additional consideration of the scissor operator to the band energies to match only experimental band gaps without correcting for valence band edge curvature, and 2. Momentum-matrix method to calculate electron group velocities. We find that the copper zinc oxide spinel is a promising dilute magnetic semiconductor, while the nickel zinc oxide spinel is a promising transparent conductor. We also compare our results on the spinel compounds to the corresponding doped zinc oxides. Thus, we have proposed improvements in materials theory that enable the discovery of new materials for photovoltaic applications.