Tailoring Nickel Oxide Thin Films: Comparative Study of Oxidizing Agents in Thermal and Plasma-Enhanced Atomic Layer Deposition.

Thermal atomic layer deposition (TALD) and plasma atomic layer deposition (PALD) were used for producing thin NiO films from nickel(II) acetylacetonate Ni(acac), employing different oxidizing agents (deionized water HO, ozone O, and molecular oxygen O). The films were deposited at 300 °C (TALD) and 220 °C (PALD) over glass substrates; their physical and chemical properties were considerably influenced by the choice of oxidizing agents. In particular, ALD(HO) samples had a low growth per cycle (GPC) and a high concentration of defects. The best NiO parameters were achieved with PALD(O), featuring high GPC (0.07 nm/cycle), high optical transparency in the visible region, electrical resistivity (1.18 × 10 Ω·cm), good carrier concentration (8.82 × 10 cm), and common mobility (5.98 cm/V·s). The resulting NiO films are polycrystalline and homogeneous in thickness and composition. According to ultraviolet photoelectron spectroscopy (UPS), work function φ and the valence band maximum can be tuned by the choice of the coreactant employed, with variations of up to ∼1 eV between TALD and PALD synthesis. Our results suggest that PALD permits one to achieve a better energy band alignment of NiO and CsFAMAPbBrI perovskite, which is promising for solar cell applications.