Pyramid scheme for brighter organic LEDs

Jun 20, 2014 by Kate Mcalpine
Jaesang Lee, Electrical Engineering PhD Student and member of the Stephen Forrest's Optoelectronic Components and Materials Laboratory, constructs a light concentrating LED in the EECS Building on May 29, 2014. The LED is able to both generate and emit light through its pyramidal shape, enabling for efficient energy use. Credit: Joseph Xu, Michigan Engineering Communications & Marketing

The most common kind of light bulb in the United States—the incandescent—is only about 5 percent efficient. The phosphorescent organic light-emitting diode, on the other hand, makes light out of 100 percent of the electricity that goes into it.

They're good for smartphone screens and mood lighting, but they drop off in both efficiency and lifetime when they have to shine brightly.

University of Michigan researchers have found an elegant way to get around this problem—by arranging the PHOLEDs into a pyramid.

"Achieving extra brightness from the conventional, flat design is inefficient and shortens the device lifetime," said Jaesang Lee, a doctoral student in and computer science and first author of the study. "However if we integrate our PHOLEDs into a pyramidal shape, we are able to achieve the equivalent, concentrated brightness at a much lower electrical current."

Because of their high efficiencies, PHOLEDs already claim much of the smartphone display market, and they are edging into televisions and ambient lighting. But when it comes to illuminating tasks like reading and detailed work, they face a disadvantage: their efficiencies and life expectancies drop off sharply when they have to shine very brightly. This happens because the easiest way to make an LED brighter is to drive it with a higher current, and this is hard on organic LEDs.

A light concentrating LED in the EECS Building on May 29, 2014. The LED is able to both generate and emit light through its pyramidal shape, enabling for efficient energy use. Credit: Joseph Xu, Michigan Engineering Communications & Marketing

The new device demonstrates a slick solution to the problem. Because PHOLEDs are naturally reflective, they serve a dual purpose when arranged on the inner surfaces of a pyramid-like structure. The PHOLEDs emit and concentrate the light that emerged from the opening at the base of the pyramid.

Although the surface area emitting light was more than four times larger than the opening at the base of the pyramid, this setup consumed about three times less electricity than trying to run a square PHOLED the size of the base at equal brightness.

The concentrator also achieves a better light distribution than a simple panel, evenly lighting flat surfaces rather than producing a bright spot in the center that dims toward the edge of the lighted area.

Jaesang Lee, Electrical Engineering PhD Student and member of the Stephen Forrest's Optoelectronic Components and Materials Laboratory, constructs a light concentrating LED in the EECS Building on May 29, 2014. The LED is able to both generate and emit light through its pyramidal shape, enabling for efficient energy use. Credit: Joseph Xu, Michigan Engineering Communications & Marketing

"My hope is that OLEDs will deeply penetrate all aspects of the lighting market because they're very efficient, very attractive and as people accept them, it will take a load off the electricity grid," said Stephen Forrest, the William Gould Dow Collegiate Professor in Electrical Engineering and leader of the study.

He says that about 30 percent of U.S. electrical usage goes to lighting, with 80 percent of that energy consumed by incandescent bulbs.

Lee's pyramidal structure resulted in illumination three times brighter than a flat configuration at the same current could have offered. Forrest thinks that smoothing out the edges and points of the pyramid into a shape more akin to a champagne flute could lead to even higher light concentrations, seven or even 10 times the brightness of a flat fixture.

An additional challenge for PHOLEDs is that some of the light gets converted to heat before it can get out of the device. As a result, laboratory PHOLEDs are about four times more efficient than incandescents but they could be 10 times more efficient. Forrest's team is also working on improving light output.

The paper, titled "Electrophosphorescent organic emitting concentrator," will be published in Light: Science and Applications.

Explore further: Scientists build thinnest-possible LEDs to be stronger, more energy efficient

add to favorites email to friend print save as pdf

Related Stories

Bright, laser-based lighting devices

Sep 27, 2013

As a modern culture, we crave artificial white lights—the brighter the better, and ideally using less energy than ever before. To meet the ever-escalating demand for more lighting in more places and to ...

Laser diodes versus LEDs

Nov 11, 2013

Solid-state lighting based on light-emitting diodes (LEDs) is the most efficient source of high color quality white light. Nevertheless, they show significant performance limitations such as the "efficiency ...

Lighting the way to the future

Sep 03, 2013

The highly inefficient incandescent light bulb is now a thing of the past, banned from European supermarket shelves in favour of more efficient lighting. The ban is part of the EU's strategy to reduce overall ...

Recommended for you

Renewable energy companies use new clout in statehouses

Dec 24, 2014

Earlier this year, Ohio became the first state to freeze a scheduled increase in the amount of electricity that must be generated by wind, solar and other renewable sources. The move gave advocates of repealing states' mandatory ...

America's place in the sun: Energy report sets goal

Dec 24, 2014

A recent energy report said that America should build on the recent growth in solar energy by setting a goal of obtaining at least 10 percent of its electricity from solar power by 2030. "Star Power: The ...

Nevada, feds to study nuke-waste burial in state

Dec 23, 2014

Nevada and the federal government are agreeing to have a panel keep studying whether the U.S. will bury radioactive material from Tennessee at a former nuclear weapons proving ground north of Las Vegas.

User comments : 5

Adjust slider to filter visible comments by rank

Display comments: newest first

DrSpock11
5 / 5 (4) Jun 20, 2014
This article is total crap.

First of all, it says that PHOLEDs are 100% efficient, which is, of course, impossible. Nothing can be 100% efficient. The article later goes on to contradict itself when it says this: "As a result, laboratory PHOLEDs are about four times more efficient than incandescents but they could be 10 times more efficient."

Second, the statement about PHOLEDs dropping off in efficiency and lifetime under high current is repeated *3 times* in the first few paragraphs. I got it after the first mention. The second two were just to bump up the word count.

Is this a science website? Is there any editorial control here at all?
byHeart
5 / 5 (1) Jun 20, 2014
One of the problems with academic research is that the patent literature is rarely consulted. In this particular case, US Patent Application US20050265404, "Luminance Enhancement Method and Apparatus" (with a priority date of May 28, 2004) discloses exactly what the University of Michigan researchers claim to have invented. (Sorry to say, but I was there ten years ago with my invention!)
Nik_2213
not rated yet Jun 20, 2014
Better send the proof-reader out for a LARGE coffee. This cascade of mistakes is almost funny...
alfie_null
not rated yet Jun 21, 2014
This article is total crap.

As is with juvenile posturing.
otero
Jun 21, 2014
This comment has been removed by a moderator.
grondilu
not rated yet Jun 22, 2014
Doesn't that just make the light more directional? I mean, like with a car headlight or something?

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.