The electronic state of thin films of yttrium, yttrium hydrides and yttrium oxide

•XPS results are reported for yttrium, yttrium oxide and reactively sputter deposited yttrium hydride films.•There is a high presence of oxide in the reactively deposited yttrium hydride films.•The electronic work function of transparent yttrium hydride has been determined to 4.76 eV.•The photochromic reaction was found to lower the electronic work function by 0.2 eV after 1 h of sunlight illumination.

Thin films of yttrium hydride have for almost 20 years been under investigation for optoelectronic and solar energy applications due to the hydrogen-induced switching in electronic state from the metallic elemental yttrium and yttrium dihydride to the transparent semiconductor material yttrium trihydride. In this study, we investigate the electronic structure of yttrium, yttrium hydride and yttrium oxide by using X-ray photoelectron spectroscopy and kelvin probe measurements. The investigated samples have been prepared by reactive sputtering deposition. We show that the electronic work function of transparent yttrium hydride is of 4.76 eV and that the recently discovered photochromic reaction lowers the electronic work function of the transparent hydride by 0.2 eV.