Self-Shading Windows – Rapidly Switching Color with Electrochromic Glass

Once the glass is switched from clear to dark, or vice versa, the new system requires little to no power to maintain its new state; unlike other materials (Khalid Abdulaziz Kaabi and Dennis Sheberla)

In order to reduce solar heat gains in a sophisticated way, it might be worth considering state-of-the-art technology like self-shading windows with electrochromic glass. This is an electronically switchable solution which blocks sunlight. By applying an electrical current, it is possible to darken the glass color at various levels. Compared to some other shading technologies, it works without moving parts. In this way, it reduces air conditioner usage in the heat of the summer. At the same time, it can be used as a barrier for privacy instead of curtains. The energy demand for the operation of this smart glass technology is very low.

Self-shading windows with electrochromic glass still an expensive luxury

However, self-shading windows with electrochromic glass are an expensive luxury. The payback period by saving energy may be disappointing owing to high investment costs. It is also problematic to achieve high levels of darkness. In addition, the darkening process is still time-consuming and takes a few minutes. Switching between total transparency and shading darkness takes time. But maybe this particular drawback is a thing of the past. Scientists at MIT found a way to switch glass from transparent to dark rapidly and keep it like this with little to no power. The findings are published in a paper which is available on Chem and published by MIT professor of chemistry Mircea Dincă and doctoral student Khalid Al-Khabbi.

Electrochromic glass with a reduced energy demand and rapid response times

Compared with other electrochromic solutions, energy is almost only needed to change the level of darkening. The change of the color depends on the applied voltage. The new method uses different photochromic materials like, for example, some eyeglasses that become darker when the light is getting brighter.

An electric current gives a negative charge to the whole window and moves the electrons. The also moving positive ions restore the electrical balance and create the color-changing effect. In contrast to the electrons, the positive ions move slower and keep the overall reaction speed low. The main change caused by using metal-organic frameworks (MOFs). These sponge-like materials speed up the process.

With the help of two mixed chemical compounds, an organic material, and a metal salt, the long-sought goal of creating a nearly black glass has been achieved as well. “It’s this combination of these two, of a relatively fast switching time and a nearly black color, that has really got people excited,” Dincă says. She adds, that no power is needed to maintain the current state or flip it back to the former state.

In order to leave the laboratory stage, the team aims to demonstrate the technology and likes to develop a 1-inch-square sample.