Screens are well known to be the biggest power consumers for electronic devices such as phones and tablets. LED (light-emitting diode) screens have become standard and are better than previous screen iterations, but they still consume a lot of power.
A big problem is that electronics produce plenty of light, but a lot of it — about 80% — gets trapped behind the screen instead of sent out to brighten the display. A University of Michigan research team is creating an electrode for OLED (organic light-emitting diode) screens that could release up to twice as much light and reduce electronic devices’ energy consumption, potentially extending their life.
“We would expect that we would get a lot of light out of an LED. But that’s the problem: Even though internally they can generate a lot of photons, only a small fraction get out to be useful light on the display,” L. Jay Guo, University of Michigan professor of electrical and computer engineering, told Centered. “We have been working on one specific problem — trying to get more light out of the devices — for a few years.”
Guo explained that a lot of energy is lost at the devices’ electrodes — anodes and cathodes — and often is wasted as heat. This happens because of a phenomenon called waveguiding, when light rays get reflected back and guided sideways into the device. They become lost in the OLED instead of coming through the screen.
“People have tried various ways to solve the problem… But when they try to solve one problem it aggravates another,” Guo said.
“We try to address the root cause. … If you can come up with a way to not let the light waveguide in the device — to kill the waveguiding function — the light can come out.”
One of the causes is a transparent electrode in between the layers of light-emitting material and the screen glass. The electrode is usually made of indium tin oxide. The Michigan researchers substituted a thin layer of transparent silver on a layer of copper. The electrode kept its functionality but eliminated the waveguiding issue.
“Silver is one of the best metals. It has low electricity loss and optical loss… [and] it makes the waveguide more difficult,” Guo said. And as an added bonus, “I think it would actually lower the cost,” he said, explaining that silver is not a rare material and the new electrode only uses a tiny amount, a layer about 5 millimeters thick.
When light rays are lost through waveguiding, electronic device screens remain dim and prompt users to turn up the brightness. This causes the screen to consume even more energy than it already does and drains the battery faster.
“If you can get good generation of this light, you can save electric power,” Guo said.
The technology could allow 40% of the light generated to flow through the screen, compared with the traditional 20%. The process becomes more energy efficient and would not drain the battery as quickly. The devices also have the potential to last longer.
The researchers have already filed for a patent. This new lab demonstration is easy to transition to the OLED manufacturing process and has generated some interest from the industry, Guo said.
“That’s very exciting about this process. It doesn’t involve any complicated patterning and creating artificial structures. It’s very compatible with current OLED manufacturing processes,” Guo said.
The team is talking with a company about doing a lab demonstration on a possible real-world application for this high-efficiency OLED. The challenge is getting manufacturers to incorporate the new technology, considering humans inherently tend to resist change. The research team is continuing to advance its innovation while talking with potential industry partners.
“This is not the end of the work. We’re moving forward and the [research] students are working hard on the next one,” Guo said. “Stay tuned.”
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