Band alignment study of the Sr1-xCaxTaO2N / H2O interface for photoelectrochemical devices and hydrogen production

Abstract

Hydrogen is one of the most promising candidates for clean energy production. Oxynitrides, like the solid solution Sr(1-x)CaxO2N, are good candidates for photoelectrochemical devices due to their low band gap that lies into the maximum zone of the solar radiation spectrum. Thus, band alignment studies in interfaces of semiconductors with water become of great importance. In this work, first-principles calculations based on density–functional theory (DFT) in the all-electron and the pseudo-potential approaches have been performed for the analysis of the band alignment in Sr(1-x)CaxO2N/H2O interfaces. A detailed study of the modelling of the surface, supercells, and interface with water molecules was done. Experimental data were taken for the structures and photoelectrochemical behaviour and well reproduced by the methodology implemented. Water structures were built from classical molecular dynamics and its electronic structure calculated using DFT. The analysis carried out led to theoretical results compatible with the experimental results and show that the partial substitution of Sr by Ca enables the gap and alignment tuning to enhance the complex performance.