# Tailoring the Hydrogen Diffusion in Polycrystalline WO3 Thin Films by a p–n Heterojunction

## TL;DR

This paper shows how adding a nickel oxide layer to tungsten trioxide thin films can control hydrogen diffusion, making it faster and more efficient.

## Contribution

The study introduces a method to enhance hydrogen diffusion in electrochromic materials using a p–n heterojunction.

## Key findings

- The depletion region at the NiO/WO3 interface acts as a barrier to hydrogen movement.
- Hydrogen diffusion is faster in the WO3/NiO layered structure compared to pure WO3.

## Abstract

This study examines
the lateral diffusion of hydrogen
in tungsten
trioxide (WO3) thin films with a nickel oxide (NiO) top
layer. It focuses on the impact of the depletion region formed at
the NiO/WO3 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 WO3 available for diffusion and increases the diffusion
velocity due to the interplay with the concentration-dependent diffusion
coefficient in polycrystalline WO3. 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
WO3/NiO layer structure compared to the pristine WO3 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.