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Highly Crystalline WO 3 Thin Films with Ordered 3D Mesoporosity and Improved Electrochromic Performance
Author(s) -
Brezesinski Torsten,
Fattakhova Rohlfing Dina,
Sallard Sébastien,
Antonietti Markus,
Smarsly Bernd M.
Publication year - 2006
Publication title -
small
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.785
H-Index - 236
eISSN - 1613-6829
pISSN - 1613-6810
DOI - 10.1002/smll.200600176
Subject(s) - materials science , crystallinity , amorphous solid , electrochromism , mesoporous material , chemical engineering , small angle x ray scattering , thin film , annealing (glass) , nanotechnology , crystallography , composite material , organic chemistry , electrode , scattering , optics , chemistry , physics , engineering , catalysis
WO 3 thin layers with nanometer‐scale periodicity were prepared by evaporation‐induced self‐assembly (EISA) using a novel amphiphilic block‐copolymer template (poly(ethylene‐co‐butylene)‐block‐poly(ethylene oxide)). The evolution of the mesoporous ordered network and the crystallinity of the framework were monitored by 2D‐SAXS, WAXS, SEM, XPS, and porosimetry. By annealing the films, the pore‐wall crystallinity is adjusted between fully amorphous and highly crystalline without mesostructural degradation. Thus, the crystalline‐film framework is composed of phase‐pure monoclinic WO 3 nanoparticles (12–14 nm in size). Furthermore, heat treatment transforms the originally spherical mesopores into ellipsoids, resulting in a unidirectionally shrunken, but still well‐defined and fully accessible bcc mesopore architecture. The influence of mesoporosity and crystallinity on electrochemical/electrochromic characteristics was addressed by monitoring electrochemical features and the absorption changes during Li insertion/extraction (repetitive potentiostatic cycling). Both the amorphous and crystalline mesoporous films possess electrochromic response times on the order of only seconds, which are attributable to the facilitated insertion of guest ions due to shortening of the diffusion path lengths. Also, the insertion/extraction reversibility of crystalline WO 3 layers with 3D mesoporosity is improved compared to amorphous ones and reaches values close to 100 %.