Atomic Layer Deposition of NiOx: Harnessing the Potential of New Precursor Combinations for Photoelectrochemical Water Oxidation

Abstract

Atomic layer deposition enables the fabrication of uniform, conformal, and pinhole-free thin films with precise sub-nanometer thickness control. This work presents the first report of thermal ALD of NiO_x using two nickel precursors –Alanis™ and [Ni(ⁱpki)₂]– in combination with two different oxidising agents (H₂O and O₃), over a temperature range of 75-250°C. The Alanis/O₃ composition exhibited one of the highest growth per cycle (1.2Å) and a broad ALD window between 100-175°C. In contrast, the Alanis/H₂O and [Ni(ⁱpki)₂]/O₃ combinations yielded lower growth rates of 0.74Å at 150°C and 0.40Å at 250°C, respectively. Comprehensive structural, morphological, optical, and chemical characterisations revealed that the choice of precursor combination and the reaction temperature significantly impact the film composition, strongly influencing its suitability for various applications. Notably, those parameters closely determined the photoelectrochemical performance and the stability of the Si/NiO_x-based photoanode towards oxygen evolution reaction. Photoelectrodes fabricated with Alanis/O₃ at 200°C demonstrate stability exceeding 24H and exhibit a remarkable OER onset potential of 1.15V vs RHE for a photocurrent density of 1mA·cm^-2.