Electrochromics for smart windows: Oxide-based thin films and devices

https://escholarship.org/content/qt6p3188fd/qt6p3188fd.pdf?t=p0him6

Electrochromic materials and devices for energy-efficient windows

Crystalline powder pellets of MoO3 and WO3 were irradiated with 253.7 nm radiation at room temperature in vacuum, in the presence of H2 and in the presence of Hg vapor and H2. Electronic changes induced in the surface of the solids were studied by x‐ray photoelectron spectroscopy. In vacuo both MoO3 and WO3 turned blue upon irradiation and the XPS spectra supported the reversible formation of +5 oxidation states which reverted upon exposure to air. When MoO3 was irradiated in the presence of H2, a hydrogen/molybdenum bronze containing Mo in the +6, +5, and +4 oxidation states and hydroxyl groups were irreversibly formed. Exposure to UV radiation in the presence of Hg vapor and H2 enhanced the formation of Mo+4 and hydroxyl groups. Irradiation of WO3 in the presence of H2 and Hg vapor/H2 mixtures produced no further reduction of tungsten compared to irradiation alone. The conclusions based upon core electron emissions from molybdenum, tungsten, and oxygen were supported by changes in the valence band spectra.

An XPS study of the UV reduction and photochromism of MoO3 and WO3

Qualitative results of an x‐ray photoelectron and optical investigation of three thin‐film transition‐metal oxides, namely, WO3, MoO3, and V2O5 are reported. Data were obtained on films that were not colored and colored by an electrochromic process. The particular electrochromic coloration process used is electrolytic in nature and employs a sandwich‐structure electrochromic cell and electrolyte pool. The optical spectra show increased absorption in the visible (red) and near‐infrared spectral regions upon coloration. The photoelectron spectra for colored films exhibit a small band near the Fermi level and asymmetric band shapes for metal core‐level bands which are absent in films that are not colored. The new band and the asymmetric band shapes are attributed to the presence of a reduced‐state species caused by the presence of trapped electrons and metal bronze formation. Results from coloration with different electrolyte pools, i.e., H+, Li+, Na+, K+, Cs+, and Mg2+ electrolytes, are reported.

Electrochromism in some thin‐film transition‐metal oxides characterized by x‐ray electron spectroscopy

Organic conducting polymers derived from substituted thiophenes as electrochromic material

X‐ray photoelectron spectra of colored WO3 films, thermodynamic analysis of galvanic behavior of the tungstic oxide cathode, plus other new lines of evidence, clearly establish the previously uncertain mechanism of the electro‐optic effect in amorphous WO3, viz., a simultaneous injection of electrons and positive ions into a film via an electrochemical process, with the consequent development of a low‐x tungsten bronze. The positive ion, in both the films and in tungsten bronzes, remains fully ionized even in the presence of high densities of injected electrons.

J. H. McGee

Papers

Mechanism of electrochromism in WO3