Imagine a computer screen that has the thickness of a sheet of paper. At one millimeter, these types of devices might only be feasible with a breakthrough in light emitting devices (LEDs). But because of the work of a University professor, this technology might be right around the corner.
Chemistry professor Stefan Bernhard has spent the past four years studying organic light emitting devices (OLEDs) — which function much like the light sources in traffic lights and some large screens like those in Times Square. Instead of using inorganic silicone, however, these devices use organic materials.
The result is an OLED with many advantages over the typical inorganic LED.
According to Bernhard, OLEDs have many advantages over other types of lights. "Currently, computer screens need a backlight like a mercury lamp that uses a lot of energy. The backlight is why when you look at the screen at an angle, the color changes," Bernhard explained. "With our displays, there is no backlight. This solves the problem of color distortion, energy loss and you could make the screen as thin as one millimeter."
Bernhard's research has been very productive. "We've published three papers just on OLEDs in the last year," he said. "We also submitted one and are working on some more."
Basic research in the field of OLEDs, however, is "waning because many big companies are getting involved. There are lots of [commercial] applications for these devices, from flexible displays to traffic lights," Bernhard said.
And OLEDs are beginning to become commercially available. Eastman Kodak announced the incorporation of OLED last March into the "world's first product featuring a full-color, active-matrix (AM) OLED display."
The OLED devices consist of a sheet of organic material, the chromophore — which is composed of iridium or ruthenium, between two electrodes. One of the electrodes is gold and the other is indium tin oxide (ITO).
"If you apply a voltage between the gold and the ITO you generate photons that are emitte.d from the chromophore," Bernhard said.
The devices Bernhard makes are two by three millimeters, barely 50 nanometers thick and cost roughly 40 cents each.
"To make a light source that works, one of the electrodes has to be transparent," Bernhard said. "ITO has such a property — it is both transparent and a good conductor of electricity. However, ITO is not an organic material and is not flexible which makes the device as a whole not truly flexible."
And that characteristic, Bernhard said, is where ITO fails in its ultimate goal.
"The chromophore is completely flexible, the gold is also completely flexible, the problem today is with the ITO," Bernhard said. "I don't know of any material — organic or inorganic — that is transparent, conducts electricity and is completely flexible at the same time."
One of the other problems with the devices is that the chromophore deteriorates very easily when a voltage is applied to it. Essentially, a few molecules react negatively, and the system stops working, Bernhard said.
"It's like that American saying, 'It only takes a few bad apples to ruin the barrel,'" he said.
Bernhard's devices can only operate for five hours before the chromophore deteriorates. "This is clearly not good for commercial applications," he said.
But he is also dealing with other problems, including color tuning.
Bernhard's research is funded by the University, which "gave [his lab] a generous starting package," he said.
The work is not restricted to flat OLED displays.
"The ultimate goal is to find devices that luminesce circularly polarized light which would be the foundation for 3-D displays," he said.
Bernhard is also trying to find a way to use similar chromophores to split water into hydrogen and oxygen gas.
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