Influence of Crystal Structure, Encapsulation, and Annealing on Photochromism in Nd Oxyhydride Thin Films

Diana Chaykina; Fahimeh Nafezarefi; Giorgio Colombi; Steffen Cornelius; Lars J Bannenberg; Herman Schreuders; Bernard Dam

doi:10.1021/acs.jpcc.1c10521

Influence of Crystal Structure, Encapsulation, and Annealing on Photochromism in Nd Oxyhydride Thin Films

J Phys Chem C Nanomater Interfaces. 2022 Feb 3;126(4):2276-2284. doi: 10.1021/acs.jpcc.1c10521. Epub 2022 Jan 24.

Authors

Diana Chaykina¹, Fahimeh Nafezarefi¹, Giorgio Colombi¹, Steffen Cornelius^{1

2}, Lars J Bannenberg¹, Herman Schreuders¹, Bernard Dam¹

Affiliations

¹ Materials for Energy Conversion and Storage, Department of Chemical Engineering, Delft University of Technology, Van der Maasweg 9, NL-2629HZ Delft, The Netherlands.
² Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology (FEP), 01277 Dresden, Germany.

Abstract

Thin films of rare earth metal oxyhydrides show a photochromic effect, the precise mechanism of which is yet unknown. Here, we made thin films of NdH_3-2x O _x and show that we can change the band gap, crystal structure, and photochromic contrast by tuning the composition (O^2-:H^-) via the sputtering deposition pressure. To protect these films from rapid oxidation, we add a thin ALD coating of Al₂O₃, which increases the lifetime of the films from 1 day to several months. Encapsulation of the films also influences photochromic bleaching, changing the time dependency from first-order kinetics. As well, the partial annealing which occurs during the ALD process results in a dramatically slower bleaching speed, revealing the importance of defects for the reversibility (bleaching speed) of photochromism.