Density Functional Theory Screening of Dopants in NiO and Mobility Limits

NiO is widely used as a hole transport layer in perovskite solar cells due to its wide bandgap, low cost, and stability. Ni vacancy defects are intentionally generated to make it ptype, but its high acceptor level requires a high concentration of defects. To identify better alternatives, we investigate a broad range of extrinsic dopants, including an alkali group and transition metals on Ni sites and group 15 elements on O sites, using density functional theory with Hubbard U correction. Among these, our results show that Li and Na form shallower acceptors than Ni vacancies. The configurational coordinate diagram shows that Ni vacancy can emit visible blue or yellow light by capturing carriers, whereas Li-doped NiO emits blue-violet light, maintaining the transparency of the material.