and Daylighting program has led a research group developing glass
devices that can change electronically from transparent to opaque.
Performing like an optical shutter, the glass is ideal for use in
making "smart windows" -- windows for buildings and cars that could
control the amount of light and heat allowed to pass through.
There is considerable commercial interest in the development of
optical switching devices. To date, 1,800 patents have been issued
on electrochromic components, one of several types of technology
under exploration. Of these patents, 1,500 are owned by Japanese
Lampert says the patent -- for a family of polymers -- would be the
first ever issued for one of the few essential elements within an
electrochromic device, an improved ion storage layer.
The pending patent is quite broad, covering 10 families of polymer
Says Lampert, "The patent carves out a major niche, making the
commercial development and marketing of electrochromic glass much
more attractive to U.S. industry." Currently, LBL's Technology
Transfer Office is seeking to license the technology to industry.
The new ion-storage electrodes -- based on polyorganodisulfides --
were the result of a collaborative effort between Lampert and
Materials Sciences Division staff scientists Steve Visco, Marca
Doeff, and graduate student Yan-Ping Mah. These novel electrode
materials are the subject of another, past patent application for
lithium polymer batteries, technology which has been licensed and
transferred to an East Bay start-up company.
Internationally, a number of alternative approaches to switchable
glass are being investigated -- liquid crystal display devices are
one example. The solid state electrochromic devices that Lampert is
developing consist of thin films that are sandwiched between two
glass sheets. They are about 100 times thinner than a human hair.
These films would allow the occupant of a building or the driver of
a car to control interior light levels as well as the flow of
infrared heat, reducing the energy necessary for lighting, heating,
and cooling. Additionally, glare could be controlled, and privacy
provided without the use of blinds or drapes.
Lampert says electrochromic devices can be likened to a thin
transparent battery. As the electrical field within the window is
changed, it optically displays its state of charge, transforming in
tint between transparent and opaque.
Switchable glass is multi-layered, with the electrochromic device
embedded inside. A window device, for example, might have glass
with an interior conductive oxide layer both on the top and bottom.
Inside of this sandwich of glass and conductive oxide is the
electrochromic device. It includes an electrochromic layer, an ion-
storage layer and between these two, an ion conductor.
Lampert says the electrochromic material tints or clears as ions
and electrons are shuttled back and forth between the
electrochromic layer and the ion-storage layer, which are akin to
two battery electrodes separated by an electrolyte. Only a small
voltage (1-2 volts DC) is required to inject or eject the ions and
"These devices have long-term memory, ranging from 12 to 48 hours,"
says Lampert. "By that I mean you can color it, remove the power,
and for that period, it will remain colored."
The first electrochromic products, rear-view auto mirrors that
automatically dim bright lights at night, are now on the market,
and switchable auto sunroofs may be available soon. But technical
obstacles to further commercial applications remain.
One stumbling block has been the ion-storage layer. The LBL
researchers believe the new polyorganodisulfide ion-storage
polymers resolve several major problems.
The ion-storage and electrochromic layers must be electrochemically
compatible with matching charge-storage capacities. Lampert and
Visco's patent application covers a family of 10 compounds that
have a range of capacities. This range provides manufacturers with
a repertoire of compatible materials. As an added bonus, it also
allows them to create tintable glass that transmits different
amounts of light.
Another advantage of the organodisulfide polymers is that they do
not shorten the life of the device.
A number of materials will act as an electrochromic electrode,
shuttling ions and electrons back and forth. But as they do so,
they gradually form insoluble compounds within the device, and
hinder its electrochemical capacity to continue to cycle between
transparent and opaque. The organodisulfide polymers can cycle back
and forth without significant degradation.
Lampert has filed a second patent for a polymer compound that
simplifies and reduces the cost of fabrication of an electrochromic
device, making it possible to combine the ion-storage and ion-
The polymer has unusual electrical characteristics. It is
electrically insulating but ion conducting. Unlike prior ion-
storage materials that were too electrically conductive, the
polymer makes it possible to dispense with the adjacent ion-
conductor layer. By eliminating this layer, fabrication is
simplified and costs reduced.
Lampert says that over the past several years, a succession of
other refinements have been made.
"In our laboratory," he says, "we have begun to make progressively
better electrochromic layers in terms of the uniformity of
coloration. Likewise, we have made improvements in the efficiency
of power usage of the devices, which can hold their charge for
longer periods than before."
Working with industry, Lampert says he is learning which remaining
problems are the most significant in terms of manufacture.
"We are receiving valuable feedback from industry, learning as well
as transferring technology we have developed. We now have workable
electrochromic components. Next," he says, "we must develop optimal
components and learn how to fabricate multilayer polymers
uniformly. When we've accomplished that, the day of smart windows
will be very near."