Excitonic, Optical, and Photovoltaic Properties of the 1T-NiO ₂ Monolayer

Developing new two-dimensional materials for photovoltaics is a central strategy to address the world’s growing energy demands. Herein, we made a multilevel, first-principles computational investigation focused on the characterization of the 1T NiO2 monolayer, evaluating its structural stability, vibrational modes and Raman spectrum, electronic, mechanical, and optical properties. Our investigation was done through first-principle calculations based on density functional theory for structural and ground state properties, complemented by many-body perturbation theory to accurately capture quasiparticle (G0W0) and excitonic effects, the latter being calculated with a maximally localized Wannier function-based tight-binding framework to describe the single particle states to solve the Bethe–Salpeter equation. Our calculations confirm that the 1T-NiO2 monolayer is energetically, dynamically, thermally (at 300 K), and mechanically stable. We found an indirect electronic band gap of 2.20 eV at the G0W0 level. Furthermore, the optical properties are dominated by strong electron–hole interactions, resulting in a direct excitonic state at 1.34 eV and an exceptionally high exciton binding energy of 880 meV. Although this optical gap is ideally positioned for solar absorption, leading to a theoretical power conversion efficiency (PCESQ) limit of 32.66%, the high exciton binding energy makes exciton dissociation into free charge carriers unfavorable. Despite the strong light absorption, the highly excitonic nature of the 1T-NiO2 monolayer makes it unsuitable for conventional photovoltaic applications but potentially promising for exciton-based optoelectronics or photocatalytic devices.