C. Edwin Tracy

Chromic Mechanism in Amorphous WO 3 Films

The authors propose a new model for the chromic mechanism in amorphous tungsten oxide films (WO{sub 3{minus}y}{center_dot}nH{sub 2}O). This model not only explains a variety of seemingly conflicting experimental results reported in the literature that cannot be explained by existing models, it also has practical implications with respect to improving the coloring efficiency and durability of electrochromic devices. According to this model, a typical as-deposited tungsten oxide film has tungsten mainly in W{sup 6{minus}} and W{sup 4{minus}} states and can be represented as W{sub 1{minus}y}{sup 6+} W{sub y}{sup 4+}O{sub 3{minus}y}{center_dot}nH{sub 2}O. The proposed chromic mechanism is based on the small polars transition between the charge-induced W{sup 5+} state and the original W{sup 4+} state instead of the W{sup 5+} and W{sup 6+} states as suggested in previous models. The correlation between the electrochromic and photochromic behavior in amorphous tungsten oxide films is also discussed.

Nanocomposite Counter Electrode Materials for Electrochromic Windows

In this paper, we describe our development of a counter electrode material that shows promise in terms of both durability and performance and is grown using common vacuum deposition methods and materials. The counter electrode films are formed by sputter deposition from a composite ceramic lithium, nickel, and tungsten oxide target. Consistent with previous reports, NiO nanocrystallites are observed to form. 12,13 Secondary phases from the other elements present in the sample are not observed, which implies that they act as substitutional or interstitial dopants or segregate to the grain boundaries and form an amorphous layer between the NiO crystallites. Experimental

Effect of Nonstoichiometry of Nickel Oxides on Their Supercapacitor Behavior

How electrochemical capacitance is affected by the non-stoichiometric properties of nickel oxide (NiO x ) films is reported. Nonstoichiometric NiO x thin-film electrodes were prepared for use in a supercapacitor by reactive radio-frequency (rf) sputtering of a nickel metal target. The oxygen partial pressure in the sputtering gas was systematically varied to fabricate various nonstoichiometric NiO x films. As the oxygen partial pressure increased in the sputtering gas, hole concentration increased from 4.7 X 10 1 6 to 1.0 X 10 1 8 cm - 3 while the specific capacitance of the NiO x films decreased from 148 to 80 F/g. A mechanism to explain the relationship between the specific capacitance and nonstoichiometry is proposed. The specific capacitance values of these NiO x films are determined by the number of Ni 2 + states that can be oxidized to Ni 3 + as a result of the double injection of OH - ions and holes.

Optimization Study of Solid‐State Electrochromic Devices Based on WO 3 / Lithium ‐ Polymer Electrolyte / V 2 O 5 Structures

Transmissive solid-state electrochromic devices based on the structure of WO[sub 3]/lithium-polymer electrolyte/V[sub 2]O[sub 5] were optimized for potential large-area window applications. The electrochromic layer thicknesses, polymer molecular weights, lithium-containing electrolytes, preassembly lithium-ion injection amounts, and transparent conductor substrates were systematically investigated for large optical modulation and fast response of the devices. The transmittance of the optimized device at 633 nm can be switched between 74 and 12% in 1 min. The coloring and bleaching voltages were [minus]1.8 and 1.2 V, respectively.

Monolithic, Self‐Powered Photovoltaic‐Electrochromic Coating for Windows

We report progress in the development of a monolithic, self-powered photovoltaic-electrochromic coating for energy-conserving windows. The coating employs an all solid-state electrochromic device based on Li-doped WO 3 as an optical transmittance modulator and a wide-bandgap amorphous SiC alloy (a-SiC:H) photovoltaic (PV) cell as an integral power source. The electrochromic device is deposited together with the PV device as a monolithic coating on a glass substrate. The active Li-ion concentration in the electrochromic device was optimized based on the thermodynamics and optical properties of the electrochromic and ion-storage layers. Electrical and electro-optic characteristics of the multilayer coatings are reported. The monolithic tandem PV-electrochromic coating shows a transmittance variation of more than 60% under 1 sun illumination.

Improving the Durability of Amorphous Vanadium Oxide Thin-Film Electrode in a Liquid Electrolyte

We report on the effects of depositing a protective inorganic solid electrolyte LiAlF 4 coating on amorphous V 2 O 5 electrode in terms of long-term cycling efficiency and stability of the V 2 O 5 in a liquid electrolyte. Two V 2 O 5 thin-film electrodes were fabricated for extensive cyclic durability testing in a LiClO 4 /propylene carbonate liquid electrolyte: One V 2 O 5 film had no overlying coating while the other had a protective thin film of solid lithium ion conducting LiAlF 4 . The protected V 2 O 5 exhibited improved durability in terms of constant capacity with repeated cycling up to 800 cycles, while the uncoated V 2 O 5 electrode displayed significant capacity loss. Our results demonstrate that deposition of an inorganic solid electrolyte (LiAlF 4 ) on amorphous V 2 O 5 films serves as a protective overlayer and enhances the long-term cycling efficiency and stability of the V 2 O 5 in a liquid electrolyte.

Lithium Thin-Film Battery with a Reversed Structural Configuration SS / Li / Lipon / Li x V 2 O 5 / Cu

All-solid-state thin-film lithium batteries were fabricated on stainless steel substrates with a reversed structural configuration of stainless steel (SS)/Li/Lipon/Li x V 2 O 5 /Cu using sequential thin-film deposition techniques. The initial thin-film battery had a cell configuration of SS/Lipon/Li 1 . 3 V 2 O 5 /Cu, During the first charging cycle, metallic Li was electroplated in between the Lipon layer and stainless steel substrate to form the anode. As corroborated by ac impedance measurements, the formation of metallic lithium anode layer was confirmed. These cells were fabricated with a 1 cm 2 active area which delivered a discharge capacity of 43 μAh/cm 2 μm at room temperature and showed a high cycle stability up to 770 cycles at a current density of 0.1 mA/cm 2 .

Electrochromic Properties of Sputtered Ni Oxide Thin Films in Acidic KCl + H2SO4 Aqueous Solutions

Electrochromic (EC) properties of sputtered Ni oxide films have been examined in KCl + H 2 SO 4 acidic aqueous solutions. KCl concentration was kept constant at 1 M while H 2 SO 4 concentrations were varied from 0 to 50 mM. EC coloration efficiency was found to be ∼30 cm 2 /C in all the solutions, and maximum charge capacity and maximum change in optical density were obtained in a I M KCl solution with 0.5 mM H 2 SO 4 . Intercalation of hydrogen ions into NiO grains is believed to be the reason for the improvement of charge capacity and optical density change. These results offer support for the practical construction of efficient complementary EC devices using dilute acidic aqueous electrolytes.

Electrochemical Supercapacitors for Optical Modulation

Amorphous hydrous ruthenium oxide thin films have been investigated and demonstrated to be an excellent optical modulating material as well as an electrochemical supercapacitor. The a-RuO 2 .xH 2 O films have been prepared by cyclic voltammetry on ITO-coated glass substrates from an aqueous ruthenium chloride solution. The cyclic voltammograms of this material show proof of capacitive behavior including two redox reaction peaks in each cathodic and anodic scan. The as-deposited a-RuO 2 .xH 2 O films exhibit an optical density change of 0.3 at 670 nm wavelength with capacitor charge/discharge in an anodic coloring fashion. This paper describes our electrochemical and electro-optical characterization results and analyses.