Recent advancements in modified porous nano-crystalline films have enabled the creation of electrochromic display or smart glass. This can be of various types.
Single Substrate Display Structure:
The single substrate display structure consists of several stacked
porous layers printed on top of each other on a substrate modified with a
transparent conductor.Each printed layer has a specific set of functions. A
working electrode consists of a positive porous semiconductor (say Titanium
Dioxide, TiO2) with adsorbed chromogens (different chromogens for different
colors). These chromogens change color by reduction or oxidation. A passivator
is used as the negative of the image to improve electrical performance. The
insulator layer serves the purpose of increasing the contrast ratio and
separating the working electrode electrically from the counter electrode. The
counter electrode provides a high capacitance to counterbalances the charge
inserted/extracted on the electrode (and maintain overall device charge neutrality).
Carbon is an example of charge reservoir film. A conducting carbon layer is
typically used as the conductive back contact for the counter electrode. In the
last printing step, the porous monolith structure is overprinted with a liquid
or polymer-gel electrolyte, dried, and then may be incorporated into various
encapsulation or enclosures, depending on the application requirements.
Displays are very thin, typically 30 micrometer, or about 1/3 of a human hair.
The device can be switched on by applying an electrical potential to the
transparent conducting substrate relative to the conductive carbon layer. This
causes a reduction of viologen molecules (coloration) to occur inside the
working electrode. By reversing the applied potential or providing a discharge
path, the device bleaches. A unique feature of the electrochromic monolith is
the relatively low voltage (around 1 Volt) needed to color or bleach the
viologens.
Viologens are toxic bi pyridinium derivatives of
4,4'-bipyridyl . [1] The name is because this class of compounds is easily
reduced to the radical mono cation, which is colored intensely blue.
Suspended Particle Devices (SPDs):
In suspended particle devices (SPDs), a thin film laminate of rod-like nano-scale particles is suspended in a liquid and placed between two pieces of glass or plastic, or attached to one layer. When no voltage is applied, the suspended particles are randomly organized, thus blocking and absorbing light. When voltage is applied, the suspended particles align and let light pass. Varying the voltage of the film varies the orientation of the suspended particles, thereby regulating the tint of the glazing and the amount of light transmitted.
SPDs can be manually or automatically "tuned" to
precisely control the amount of light, glare and heat passing through, reducing
the need for air conditioning during the summer months and heating during
winter. Smart glass can be controlled through a variety of mediums, such as
automatic photosensors and motion detectors, smartphone applications,
integration with intelligent building and vehicle systems, knobs or light
switches.
Smart glass light-control technology increases users'
control over their environment, provides for better user comfort and well-being
and improves energy efficiency. The technology provides over 99% UV blockage
and state switching in 1 to 3 seconds. In cars, the range of light transmission
for the technology is 50-60 times darker than a typical sunroof to twice as
clear as an ordinary sunroof. Published data by Mercedes-Benz shows that SPD
technology can reduce cabin temperatures inside a vehicle by 18 °F (10 °C).
Other advantages include reduction of carbon emissions and the elimination of a
need for expensive window dressings.