E. Avendaño

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.

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.

Properties of electrochromic nickel-vanadium oxide films sputter-deposited from nonmagnetic alloy target

In this study we investigate the structure, composition, diffusion coefficient, and electrochromic properties of nickel-vanadium oxide films as a function of deposition conditions. Polycrystalline films have been deposited by DC magnetron sputtering from a nonmagnetic target of Ni0.93V0.07 in an atmosphere of O2/Ar and Ar/O2/H2, with the gas flow ratios varied systematically to cover the range from nearly-metallic to overoxidized films. The results contradict the usual view that films deposited in O2/Ar are dark brown in their as-deposited state. While such films can easily be deposited, the optimum electrochromic properties have been observed at O2/Ar ratios giving nearly transparent films. Addition of hydrogen to the sputtering atmosphere improved cycling stability of the films. The diffusion coefficient has been determined by the Galvanostatic Intermittent Titration Technique (GITT).

Investigation of indirect structural and chemical parameters of GeSi nanoparticles in a silica matrix by combined synchrotron radiation techniques

The formation of GeSi nanoparticles on an SiO2 matrix is studied here by synchrotron-based techniques. The shape, average diameter and size dispersion were obtained from grazing-incidence small-angle X-ray scattering data. X-ray diffraction measurements were used to obtain crystallite sizes and composition via resonant (anomalous) measurements. By using these techniques as input for extended X-ray absorption fine structure analysis, the local composition surrounding the Ge atoms is investigated. Although the results for each of the methods above are commonly analyzed separately, the combination of such techniques leads to an improved understanding of nanoparticle structural and chemical properties. Crucial indirect parameters that cannot be quantified by other means are accessed in this work, such as local strain, the possibility of forming core–shell structures, the fraction of Ge atoms diluted in the matrix (not forming nanoparticles), the amorphous and crystalline Ge fractions, and the relative population of nanoparticles with single and multiple crystalline domains.

Electrochromic materials and their applications in foil-based devices

Electrochromic films based on oxides of W, Ni, and Ir were made by reactive DC magnetron sputtering. Enhancements of the bleached-state transmittance, by adding Al or Mg to oxides of Ni or Ir, were documented. Sputtering of W oxide in the presence of hydrogen, and post-deposition treatment of Ni oxide in ozone, produced charge balancing of the components of the electrochromic device in a way that enabled facile assembly by lamination.

Chromogenics for Sustainable Energy : Some Advances in Thermochromics and Electrochromics

Chromogenic materials are able to change their optical properties in response to external stimuli such as temperature (in thermochromic materials) and electrical charge insertion (in electrochromic materials). Below we review some recent advances for these types of materials. Specifically we first discuss the limitations of thermochromic VO2 films for energy efficient fenestration and show from calculations that nanocomposites containing VO2 can have superior properties and display high luminous transmittance and large temperature-dependent solar transmittance modulation. Even better results may be found for nanoparticles of VO2:Mg. In the second part of the paper we survey some recent progress for electrochromic devices and show that W oxide films have increased coloration efficiency when some Ni oxide is added. We also present initial results for flexible electrochromic foils produced by roll-to-roll coating and continuous lamination.