The dependence of structural, electrical and optical properties on the composition of photochromic yttrium oxyhydride thin films

Abstract Thin films of yttrium oxyhydride (YHO) exhibit reversible light-induced resistivity and transmission changes at room temperature and ambient pressure. Establishing how the physical properties of YHO films are influenced by their chemical composition is an important challenge that can open the way toward practical applications. In this work, we have prepared YHO thin films with lateral gradient of oxygen and hydrogen concentrations by reactive magnetron sputtering deposition. This enables us to efficiently investigate the effect of changes in the composition of the films on their structural, electrical and optical properties. The as-deposited YHO film appeared to be black opaque and non-photochromic in the oxygen-poor part of the film, and it changed to yellow transparent and photochromic in the oxygen-rich part of the film. We report a gradual increase in the lattice constant with increasing oxygen content of the film, as revealed by grazing incidence X-ray diffraction measurements. Electrical resistivity measurements unveiled that persistent photoconductivity was strongly enhanced as the oxygen content decreased in the photochromic yellow transparent film. Analysis of the kinetics of the photochromic reaction indicated that the bleaching speed increased with increasing oxygen content in the photodarkened film. Unusual large persistent photochromism was discovered in the same yellow YHO film with lowest oxygen content which lasted for almost 10 days. Moreover, it was shown that the optical constants can be tuned by varying the oxygen content in the photochromic film as well.