Electrochromic smart glasses help achieve the objectives of the European Climate Law by enabling control over energy usage, glare, and comfort by the alteration of their tint level in response to an electrical signal.
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Smart glasses that are electrochromic (EC)
When an electrical signal is applied to electrochromic smart glass, it modifies its transmittance, or the amount of light it lets through. The glass can become opaque or transparent (or any condition in between) as a result of this reversible alteration. The typical layout of an electrochromic cell is shown below:
Sort of Like a Battery
The figure illustrates that an electrochromic glass panel is made up of many layers. Using the same physical vapour deposition (PVD) method as the semiconductor manufacturing sector, this stack is typically a few microns thick, or a few thousandths of a millimeter.
Transparent conductive layers, often made of indium tin oxide (ITO), are present on the exterior glass panels. These layers transform the entire structure into something like to a battery, with the ITO serving as the electrodes.
The ion storage layer, ion conductor (electrolytic) layer, and electrochromic (EC) layer are located in the center of the structure and together are in charge of the transmittance change.
Charged particles, usually lithium ions, move from the ion storage layer through the electrolyte and into the electrochromic layer (typically tungsten oxide, which is transparent when it is not active) when a direct current (DC) voltage is applied to the system. This leads in the electrochromic layer going through electrochemical reduction-oxidation, or redox, which absorbs light and gives it color. The glass regains its transparency when the voltage is reversed because the lithium ions migrate back from the electrochromic (EC) layer, via the electrolyte, and back to the ion storage layer. The time frame for this state transition might be minutes. If you want to go further into this topic
Why does the transmittance of electrochromic glass change?
Lithium ions will “intercalate,” or insert themselves into, the electrochromic layer when a voltage is supplied across the electrochromic stack. The tungsten oxide’s “band gap” is reduced by the inserted lithium ions to around 2 electron-Volts (eVolts). This implies that photons with an energy of at least that amount may be absorbed by the tungsten oxide, hence energizing electrons into a higher energy state. Photons of visible light, which possess at least this energy, are absorbed by the intercalated electrochromic layer. As a result, solar radiation that enters the human eye via the glass appears to be deficient in certain wavelengths, resulting in a lack of visible light and a colored appearance.
Electrochromic Memory and Device Architectures
There are several electrochromic device architectures, including:
Electrochromic hybrid
Hybrid electrochromic glass, which combines an organic (polymer) electrolyte with an inorganic electrochromic layer, may maintain its state for four to five days, demonstrating a memory function [3]. However, leakage limits the charge retention, which leads to the ultimate clear return of the EC glass. Power is only needed for the memory capability when it changes states. Conversely, as long as they are kept in their transparent states, SPD and PDLC smart glass technologies need to be charged constantly.
Superconducting Electrochromic
Solid-State EC glass, which is perfect for building facades, has a lifespan of around 20–30 years while lacking memory capacity. It has been shown to be extremely robust in cycle testing conducted under harsh temperature conditions and UV exposure.
What Makes Low Voltage Such a Big Deal?
According to European standard EN 60335, the IET classifies a product as a “Safety Extra-Low Voltage” (SELV) device if its operating voltage is less than 60Vdc. This is crucial because cables will need to be run to the electrochromic glass, which is frequently mounted into the face of buildings or vehicles (think: cars, yachts, and airplanes). The safety risk decreases and cable cost decreases with decreasing voltage and current. You can see how lower-voltage solutions may save installation and operating maintenance expenses for a large-scale smart glass installation.
One Final Item: Time
It should be emphasized once more how much slower electrochromic smart glasses are than SPD and PDLC smart glasses (which change states in a matter of seconds). Electrochromic smart glasses take minutes to change states. This gradual transition can be advantageous in architectural applications because it gives our eyes time to acclimate to the gradual change in light level. Additionally, buildings might benefit from a modest, progressive alteration of their front rather than abrupt modifications that could be distracting to onlookers, vehicles, or wildlife. This gradual shift might be detrimental to mobility or possibly a safety concern because visibility depends on being able to see outside the car. The advantages of reducing heat and glare using low-cost, lightweight cabling that operates at a safe low voltage, however, could outweigh this problem.
So, Do I Really Need Electrochromic Glass?
This will rely on the cost vs. benefit analysis for the building, car, or consumer gadget’s development as well as the ongoing operating expenses. For electrochromic smart glasses to become widely accepted, their cost and switching times must be significantly lowered. Of course, the 30% tax credits provided by the US Dynamic Glass Act will be helpful, but this is only a short-term solution (until January 1, 2025). The dynamic heat rejection characteristics, when combined with low energy consumption and safe voltages, may be more significant and might be the deciding factor in many applications.
