# Thermally Engineered Nickel-Tungsten Oxide Films for Energy Efficient Electrochromic Devices

## TL;DR

This paper explores how adjusting the temperature during film deposition can improve the performance of smart window materials.

## Contribution

The study demonstrates that lower substrate temperatures enhance electrochromic performance through increased nickel vacancies and amorphous structure.

## Key findings

- Films deposited at lower temperatures show 64% optical contrast and fast coloration/bleaching dynamics.
- Amorphous structure and nickel vacancies improve lithium-ion transfer efficiency.
- Substrate temperature regulation effectively tunes microstructure and defect chemistry.

## Abstract

Nickel-oxide-based anodic electrochromic materials are extensively utilized as counter electrodes in smart window systems due to their reversible optical response during ion insertion and extraction. This study systematically investigates the influence of substrate temperature on the electrochromic properties of sputtered nickel-tungsten oxide thin films. The deposited thin films exhibit an amorphous structure. An increase in substrate temperature results in a decrease in nickel-vacancy concentration. Raman spectroscopy verifies the amorphous nature. Films deposited at lower substrate temperatures exhibit superior electrochromic performance, characterized by improved optical contrast of 64% and rapid coloration (2.21 s) and bleaching (0.93 s) dynamics. The enhanced performance is ascribed to the disordered amorphous structure and the existence of enough nickel vacancies, which collectively facilitate efficient and reversible lithium-ion transfer. This study illustrates that meticulous regulation of substrate temperature is an effective method for adjusting the microstructure and defect chemistry of nickel–tungsten oxide thin films, rendering them appropriate as effective counter electrodes for energy-efficient smart window applications.