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Utah researchers suggest OLED efficiency not so hot

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[Image credit: University of Utah]
The LEDs you see in use all over these days — in traffic lights, flashlights, and all over your computer — are able to convert somewhere between 50 and 70 percent of the energy passed to them into light. This high efficiency makes them ideal for those purposes mentioned, but high costs have prevented them from replacing other types of lighting completely; fluorescent is still much more cost-effective. Organic LEDs, however, which are made of organic or “plastic” (?) materials, promise to be much cheaper to make, and may be cheap enough to replace traditional lighting in most situations. Everyone’s excited about OLEDs, but new research suggests there may be complications.

The problem is that for years OLEDs have had a theoretical ceiling of 25 percent efficiency, meaning that though costing less, they’d use twice as much power as inorganic LEDs. Some researchers have theorized ways in which OLEDs might achieve comparable efficiency as inorganics, but research by University of Utah materials scientists suggests that the 25 percent figure is probably correct. This doesn’t mean OLEDs are out of luck; they have a lot of advantages: in addition to their lower price, they have better color range and viewing angle, and are capable of being put on flexible materials. Chances are neither type of LED is going to squish the other since they have unique features.

The researchers were also looking into spintronic/quantum computing and found they could control a current via the spin of an electron, but that is neither here nor there. [via Physorg]

Update: J. Levine informs us in tips that while fluorescent OLEDs have a low ceiling efficiency, phosphorescent OLEDs approach 100% efficiency. The article he links to states:

We demonstrate very high efficiency electrophosphorescence in organic light-emitting devices employing a phosphorescent molecule doped into a wide energy gap host. Using bis(2-phenylpyridine)iridium(III) acetylacetonate [(ppy)2Ir(acac)] doped into 3-phenyl-4(1[prime]-naphthyl)-5-phenyl-1,2,4-triazole, a maximum external quantum efficiency of (19.0±1.0)% and luminous power efficiency of (60±5) lm/W are achieved. The calculated internal quantum efficiency of (87±7)% is supported by the observed absence of thermally activated nonradiative loss in the photoluminescent efficiency of (ppy)2Ir(acac). Thus, very high external quantum efficiencies are due to the nearly 100% internal phosphorescence efficiency of (ppy)2Ir(acac) coupled with balanced hole and electron injection, and triplet exciton confinement within the light-emitting layer.

Yikes! Now, If I’m honest, I had no idea there were two fundamentally different types of OLEDs. I’m thinking that, since the article I read did not specify (that I saw at least) fluorescent, then it must have been assumed; perhaps over the years since the 2001 article was published fluorescent OLEDs have become the default due to price or some other force. Certainly Mr. Levine is correct, but I think that the U of U study was using the most readily available or cheapest types of OLEDs, which are almost certainly what would be used by the industry if put into true mass production. Thanks for keeping us honest.

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