Abstract
This study examines the lateral diffusion of hydrogen in tungsten trioxide (WO(3)) thin films with a nickel oxide (NiO) top layer. It focuses on the impact of the depletion region formed at the NiO/WO(3) p-n heterojunction on the diffusion process. This depletion region influences diffusion by acting as a barrier to hydrogen movement. It effectively reduces the thickness in WO(3) available for diffusion and increases the diffusion velocity due to the interplay with the concentration-dependent diffusion coefficient in polycrystalline WO(3). Our in situ measurement technique allows for the detailed study of lateral hydrogen diffusion by inducing a concentration gradient in the layer plane. This method demonstrates by a direct comparison that diffusion is faster in the WO(3)/NiO layer structure compared to the pristine WO(3) structure. This research demonstrates the technological potential of manipulating and tuning diffusion processes in electrochromic materials by incorporating them in layered structures and paves the way for more advanced applications.