Electrochromic and Thermochromic

Electrochromic and Thermochromic

Chromogenic Materials

Glazing materials that selectively control the spectral aspect of radiation are now commonplace. Low-emittance coatings suppress infrared radiation transfer thereby imparting additional thermal insulation. Modified low-emittance coatings can also reject unwanted heat gain due to solar infrared. Additional energy savings result with dynamic control over the spectral characteristics of the glazing. There are a variety of technologies that can produce the desired effect

Transition Metal Switchable Mirror

The switchable-mirrors technology was developed by Tom Richardson and Jonathan Slack of the Energy Technologies Area at Berkeley Lab. By using transition metals rather than the rare earth metals used in the first metal-hydride switchable mirrors, Richardson and Slack were able to lower the cost and simplify the manufacturing process. Energy performance is improved as well, because the new windows can reflect or transmit both visible and infrared light. Besides windows for offices and homes, possible applications include automobile sunroofs, signs and displays, aircraft windows, and spacecraft.

See the mirror windows in action on this Youtube video: www.youtube.com/watch?v=f_YJkb1fHQw.


Considered to be the most suitable chromogenic technology for energy control in buildings, electrochromics are the subject of intensive research. Electrochromic materials undergo a reversible change in optical properties upon injection of light ions. Typically they consist of two electrodes separated by an ion conductor. Transparent conductors form the contacts. We have an active research program focusing on complementary counterelectrodes in lithium-ion systems. Association with the Berkeley Electrochemical Research Center provides a constant flow of new ideas for materials.

Measurement of optical properties is a specialty, and we have an extensive library of optical indices of electrochromic materials. Realistic images generated by Radiance have been used to visualize an electrochromic office and determine light levels under various conditions. DOE also supports an Electrochromics Initiative whose purpose is to accelerate the development of a window product.


As the name implies, these materials darken under the direct action of sunlight. They are not considered as versatile as electrochromics because they cannot be manually controlled and because optimum energy performance requires consideration of temperature conditions as well as solar radiation. For example, a photochromic window may darken on a cold sunny day when more solar heat gain is desirable. They are used widely for automatically darkening sunglasses as shown at corning.com. This is also an illustration about how our primary goal is to assist industry in developing new products.


As photochromics respond primarily to light, thermotropics respond to heat. Again this is not as versatile a response as electrochromics. Daylight or view may have a higher priority for the occupant, at least temporarily, than reduction in solar gain.

Principal Investigator(s)

Andre Anders