Highly crystalline WO3 thin films with ordered 3D mesoporosity and improved electrochromic performance
Torsten Brezesinski1, Dina Fattakhova Rohlfing, Sébastien Sallard
1Max Planck Institute of Colloids and Interfaces, Research Campus Golm, Am Mühlenberg 1, 14476 Potsdam-Golm, Germany. Torsten.Brezesinski@mpikg-golm.mpg.de
Small (Weinheim an Der Bergstrasse, Germany)
|December 29, 2006
Summary
Tungsten oxide (WO3) thin films with tunable crystallinity were created using self-assembly. These mesoporous WO3 films exhibit fast, reversible electrochromic properties, ideal for advanced optical devices.
Area of Science:
- Materials Science
- Nanotechnology
- Electrochemistry
Background:
- Tungsten oxide (WO3) is a promising material for electrochromic applications.
- Controlling the nanostructure and crystallinity of WO3 thin films is crucial for optimizing their performance.
- Evaporation-induced self-assembly (EISA) offers a route to create ordered mesoporous materials.
Purpose of the Study:
- To synthesize WO3 thin layers with controlled mesoporosity and crystallinity using a novel block-copolymer template.
- To investigate the structural evolution and properties of these WO3 films.
- To correlate mesostructure and crystallinity with electrochemical and electrochromic behavior.
Main Methods:
- Evaporation-induced self-assembly (EISA) with a poly(ethylene-co-butylene)-block-poly(ethylene oxide) template.
- Characterization using 2D-SAXS, WAXS, SEM, XPS, and porosimetry.
- Electrochemical and electrochromic performance evaluation via potentiostatic cycling and absorption monitoring.
Main Results:
- Achieved WO3 thin films with nanometer-scale periodicity and tunable pore-wall crystallinity (amorphous to crystalline) via annealing.
- Crystalline films featured phase-pure monoclinic WO3 nanoparticles (12-14 nm) and transformed spherical mesopores into ellipsoidal, accessible bcc structures.
- Both amorphous and crystalline mesoporous films showed rapid electrochromic response (seconds) due to shortened ion diffusion paths.
- Crystalline WO3 films demonstrated improved Li insertion/extraction reversibility (near 100%) compared to amorphous films.
Conclusions:
- EISA is effective for creating tunable mesoporous WO3 films with controlled crystallinity.
- Mesoporous structure and crystallinity significantly influence electrochromic performance, enhancing response speed and reversibility.
- These findings pave the way for developing advanced electrochromic materials with tailored properties.
