In the past decade the development of technology was amazing and very fast. The development happens with the cause of making our lives better and of higher quality. Electrochromic smart windows were made with this purpose and we got to control one more acpect, this time the control of the amount of light and heat passing through our windows.
Basics:
Smart glass, EGlass, or switchable glass, also called smart windows or switchable windows in its application to windows or skylights, refers to electrically switchable glass or glazing which changes light transmission properties when voltage is applied.
Certain types of smart glass can allow users to control the amount of light and heat passing through: with the press of a button, it changes from transparent to translucent, partially blocking light while maintaining a clear view of what lies behind the window. Another type of smart glass can provide privacy at the turn of a switch.[1]
This paper covers three aspects of electrochromic smart windows. Their energy efficiency is discussed, and it is argued that a control strategy considering whether a room is in use or not can lead to large savings of the energy needed for space cooling. With regard to durability, it is shown that chemical compatibility between the electrolyte and electrochromic films of tungsten oxide and nickel oxide can be achieved without loss of optical transparency. Finally, we consider device manufacturability and present data on precharging of electrochromic nickel oxide films by ozone treatment. [2]
A potential driven self-assembly of sodium dodecyl sulfate/tungsten oxide aggregates at the electrolyte–electrode interface followed by template extraction and annealing yielded mesoporous thin films of electrochromic tungsten oxide (WO3). Electron microscopy images revealed that the films are characterized by a hitherto unreported hybrid structure comprising nanoparticles and nanorods with a tetragonal crystalline phase of WO3 with the measured lattice parameters: a = 0.53 nm and c = 0.37 nm. In addition to pentagonal voids characteristic of the tetragonal WO3 phase at the lattice scale, open channels and pores of 5–10 nm in diameter lie between the nanoparticles, which cumulatively promote rapid charge transport through the film. This resulted in colouration efficiency (ηmax~90 cm2 C−1 at λ = 900 nm) and switching kinetics (colouration time = 3 s and bleaching time = 2 s for a 50% change in transmittance) higher and faster than previously reported values for mesoporous WO3 films. Repetitive cycling between the clear and blue states has no deleterious effect on the electrochromic performance of the film, which is suggestive of its potential as a cathode in practical electrochromic windows. [3]
Titanium doped tungsten oxide thin films have been deposited by co-sputtering metallic titanium and tungsten in the presence of argon and oxygen. The oxygen chamber pressure was varied in the range 1 × 10− 3–4 × 10− 3 mbar keeping the sputtering power of titanium and tungsten constant at 2 W/cm2 and 3 W/cm2 respectively. The effect of oxygen chamber pressure on the electrochromic (EC) properties of titanium doped WO3 has been investigated in three steps. First, the material properties of EC film were investigated by XRD, SEM, and UV–Vis spectrophotometer; the thickness and the optical constants were estimated from the reflectance measurements. Second, the electrochromic behavior of the EC films was characterized by cyclic voltammetry (CV) using 1.0 M HCl as electrolyte. The optical modulation (ΔT) and coloration efficiency (CE) of the titanium doped tungsten oxide thin film deposited at an O2 pressure of 4 × 10− 3 mbar was found to be better with typical values of ΔT = 70% and CE = 66 cm2/C (at λ = 550 nm). Finally, EC devices consisting of five layers (Glass/ITO/Ti:WO3/Ta2O5/NiO/ITO) have been fabricated and tested. [4]
A novel nanocomposite lithium ion-conducting electrolyte has been developed, based on organically modified silanes, which is suitable for application in a sol-gel electrochromic system. The system developed consists of FTO-coated (fluorine doped tin oxide) glass coated with tungsten oxide, WO3, at one side of the device as the electrochromic layer, with a cerium oxide-titanium oxide layer, CeO2-TiO2, acting as ion-storage layer or counter electrode. The adhesive properties of the electrolyte enabled the manufacture of electrochromic devices in a laminated structure: glass\FTO\WO3\nanocomp.elect.\CeO2-TiO2\FTO\glass. The conductivity of the nanocomposite electrolyte system varies between 10-4 and 10-5 Scm-1 at 25 degrees Celsius depending on the exact composition. The temperature dependence of the conductivity exhibits typical Vogel-Tamman-Fulcher (VTF) behavior. The thickness of the electrolyte between the two halves of the device could be adjusted by the use of a spacer technique in the range 10 – 150 micrometer. At present, cells are constructed in two formats: 10 multiplied by 15 cm2 and 35 multiplied by 35 cm2. Switching times under one minute were achieved for the smaller format with a corresponding optical modulation between 75% to 20% (at lambda equals 0.633 micrometer). In the case of the larger format the switching time increases to several minutes due to the increase in geometric area. [5]
Conclusion:
Electrochromic smart windows have been a sort of a break through when it comes to windows and their quality. They let us control how much heat or light we want to let in our house or flat. They are easy to operate on and pleasing to the eye. The development of electrochromic smart windows is continuing.
References:
[1] http://en.wikipedia.org/wiki/Smart_glass
[2] “Electrochromic smart windows: energy efficiency and device aspects” by: A. Azens and C. Granqvist
[3] ”Nanostructured mesoporous tungsten oxide films with fast kinetics for electrochromic smart windows” by: M Deepa, A K Srivastava, K N Sood and S A Agnihotry
[4] ”Studies on electrochromic smart windows based on titanium doped WO3 thin films” by: A. Karuppasamy, , A. Subrahmanyam
[5] ”Development of electrochromic smart windows by sol-gel techniques” by: Bruce S. Dunn, John D. Mackenzie, Edward J. A. Pope, Helmut K. Schmidt, Masayuki Yamane
Special thanks goes to http://www.rivercitymackay.com/ for “Electrochromic smart windows” suggestion.
