First-Principles Study on Doping of Copper Halides

We investigate the doping behavior of copper halides CuX ( X = Cl, Br, and I) by using density functional theory calculations. We evaluate the formation energies of Cu and X vacancies, which reveal the formation of Cu vacancies to be energetically favorable when the Fermi level is near the valence band maximum, leading to the p-type conductivity of Cu X. The possible hole concentration of Cu X due to the formation of vacancies is predicted to decrease from CuI to CuBr and CuCl, consistent with experiments. We also study hydrogen interstitials, which show that the p-type conductivity of Cu X , especially CuCl, can be undermined due to compensation of holes by hydrogen interstitials. By inspecting the band offset of Cu X , we provide fundamental insights into the X dependence of p-type doping in Cu X .