A. Azens

Electrochromic coatings and devices: survey of some recent advances

The first part of this paper reviews a large number of electrochromic devices for modulating transmittance and emittance. Data are given on all-solid-state devices as well as on polymer laminated devices, with and without self-powering by integrated solar cells. In the second part we turn to a specific, flexible polyester-based device incorporating electrochromic W oxide and Ni oxide and discuss, among other things, gas treatments for precharging of the individual electrochromic films in order to make them ready for facile device assembly, and enhancements of the bleached-state transmittance through addition of Al or Mg to the Ni oxide.

Recent advances in electrochromics for smart windows applications

Electrochromic smart windows are able to vary their throughput of radiant energy by low-voltage electrical pulses. This function is caused by reversible shuttling of electrons and charge balancing ions between an electrochromic thin film and a transparent counter electrode. The ion transport takes place via a solid electrolyte. Charge transport is evoked by a voltage applied between transparent electrical conductors surrounding the electrochromic film/electrolyte/counter electrode stack. This review summarizes recent progress concerning: (i) calculated optical properties of crystalline WO3, (ii) electrochromic properties of heavily disordered W oxide and oxyfluoride films produced by reactive magnetron bias sputtering, (iii) novel transparent reactively sputter-deposited Zr–Ce oxide counter electrodes and (iv) a new proton-conducting antimonic-acid-based polymer electrolyte. Special in depth presentations are given on elastic light scattering from W-oxide-based films and of electronic band structure effects affecting opto–chronopotentiometry data in Zr–Ce oxide. The review also contains some new device data for an electrochromic smart window capable of very high optical transmittance.

Sputter-deposited nickel oxide for electrochromic applications

Thin films were produced by sputtering of metallic Ni in Ar/O-2 and Ar/O-2/H-2 atmospheres. Systematic studies of these films were carried out in electrochromic devices with tungsten oxide and e ...

Towards the smart window : progress in electrochromics

Electrochromic devices have the ability to produce reversible and persistent changes of their optical properties. The phenomenon is associated with joint ion and electron transport into/out of an electrochromic thin film, in most cases being a transition metal oxide. This paper outlines the various applications of such devices in smart windows suitable for energy-conscious architecture, in variable-reflectance mirrors, and in display devices. Critical materials issues and design concepts are discussed. The paper also covers two specific research topics: computed electronic structure of crystalline WO3 incorporating ionic species, showing how reflectance modulation emerges from a first-principles calculation; and Li+ dynamics in heavily disordered Ti oxide, illustrating how diffusion constants derived from impedance spectroscopy can be reconciled with the Anderson—Stuart model.

Polaron absorption in amorphous tungsten oxide films

Amorphous thin films of tungsten oxide were deposited by sputtering onto glass substrates covered by conductive indium–tin oxide. The density and stoichiometry were determined by Rutherford backscattering spectrometry. Lithium ions were intercalated electrochemically into the films. The optical reflectance and transmittance were measured in the wavelength range from 0.3 to 2.5 μm, at a number of intercalation levels. The polaron absorption peak becomes more symmetric and shifts to higher energies until an intercalation level of 0.25 to 0.3 Li+/W, where a saturation occurs. The shape of the polaron peak is in very good agreement with the theory of Bryksin [Fiz. Tverd. Tela 24, 1110 (1982)]. Within this model, the shift of the absorption peak is interpreted as an increase in the Fermi level of the material as more Li ions are inserted.

Electrochromic devices embodying W oxide/Ni oxide tandem films

Six-layer electrochromic devices of indium tin oxide (ITO)/NiOxHy/WO3/ZrP-electrolyte/WO3/ITO were made by reactive dc magnetron sputtering and lamination. The WO3 layer between the acidic ZrP-based electrolyte and the NiOxHy layer served as optically passive protective layer. The optical inactivity of the protective layer could be understood from arguments based on electron density of states.

Angular selective transmittance through electrochromic tungsten oxide films made by oblique angle sputtering

Tungsten oxide films were made by magnetron sputtering with a large angle between the substrate normal and the direction of the deposition flux. Scanning electron microscopy displayed a microstructure composed of inclined columns. Spectrophotometric measurements on films with different amounts of electrochemically intercalated Li+ ions showed pronounced angular selective transmittance together with electrochromism.

Ozone coloration of Ni and Cr oxide films

Films of Ni and Cr oxide were made by reactive DC magnetron sputtering. Ozone exposure, obtained by ultraviolet irradiation in the presence of oxygen, gradually induced coloration in the initially transparent films. Electrochemical measurements correlated the optical absorption with a charge deficiency in the film. Our results demonstrate a convenient technique for treating the counter electrode in a W-oxide-based electrochromic device prior to device assembly.

Proton Diffusion and Electrochromism in Hydrated NiOy and Ni1-xVxOy Thin Films

Electrochromic hydrated nickel oxide and nickel vanadium oxide thin films were deposited by reactive dc magnetron sputtering. Optical modulation was effected by insertion and extraction of protons. The proton diffusion coefficient D during the insertion/ extraction process was determined by galvanostatic intermittent titration. We analyzed D as a function of changes in the stoichiometry and found deep minima at certain H/Ni ratios. These minima were interpreted, within the bleached state, as due to a structural phase transition from (3-nickel hydroxide to α-nickel hydroxide. The optical absorption increased rapidly at the H/Ni ratio corresponding to the second phase transition. At the transition to the colored state, our data were consistent with a structural phase transition from α-nickel hydroxide to γ-nickel oxy-hydroxide, in accordance with the Bode reaction scheme. Those structural changes were corroborated by infrared reflection-absorption spectroscopy.

Transparent ion intercalation films of Zr–Ce oxide

Zr–Ce oxide films were made by reactive dc magnetron cosputtering. The elemental composition was determined by Rutherford backscattering spectrometery and the crystalline structure by x-ray diffraction. Li intercalation/deintercalation was accomplished potentiodynamically in a liquid electrolyte. The films remained fully transparent irrespective of their degree of lithiation, which may be reconciled with a population/depopulation of Ce 4f levels.