High-tech light shutter could help turn your windows into LCD displays
Researchers at the Pusan National University in South Korea have developed an advanced light shutter that can rapidly switch between transparency and opaqueness in less than a millisecond, paving the way for displays that become see-through at the flick of a switch.
Most transparent displays rely on organic light emitting diodes (OLEDs). Such displays would ideally be completely transparent when turned off, but also completely opaque when turned on, so that whatever is behind the screen can’t disturb picture quality.
Pixels in see-through OLED displays are made of a transparent and a light-emitting component, but the transparent part is always open to the background, and this can make the display very hard to read. The remedy is to use microscopic shutters that block light and make the display opaque when turned on. But the two types of shutters developed so far – based on light scattering or absorption – are either not entirely opaque, or unable to provide black color. They’re also energy-hungry, requiring electricity to remain see-through, and take a long time to switch on and off.
Professor Tae-Hoon Yoon and team have developed a shutter that solves these problems by combining scattering- and absorption-based shutters in a single device, using liquid crystal cells containing dichroic dyes.
Light (red lines in the picture above) is first scattered by a network of polymers and then absorbed by the dyes, which are surrounded by electrodes. When electricity is applied to the electrodes, the dye molecules align with incoming light, scattering it and making the display fully opaque. When power is turned off, the molecules are aligned perpendicularly to the electrodes, making the display transparent.
Because the shutters can be activated through an electric field, they can be switched on and off in less than a millisecond. They also have low power requirements, requiring energy only to become opaque but not to stay transparent.
Next up, Yoon and colleagues will work on developing a bistable version of the shutter that only consumes power when switching between opaque and transparent, which would bring the dream of practical transparent displays even closer to reality.
A paper on the study was published in the scientific journal AIP Advances.