mannerisms

Ruminations on the electronics industry from David Manners, Senior Components Editor on Electronics Weekly.

Fipels Take On LEDs

Fipel (field-induced polymer electroluminescent) lighting could replace LEDs and fluorescent lighting. First production is expected next year.

Invented by David Carroll, Professor of Physics at Wake Forest University, North Carolina, Fipels use three layers of light-emitting polymer which contain traces of nanomaterials which glow when a current is applied.

 

Fipels have a  planar light emitting structure energised by an AC field from insulated electrodes. They  can be made in any shape with any tint to the white light, says Dr Carroll, who says he’s made one which has lasted ten years.

 

There is no junction. Instead the key component is a layer of polymer loaded with an iridium compound and doped multi-wall carbon nanotubes.

 

“The AC stimulates displacement current in the polymer, in which we have placed charge sources and field sinks from nano-materials,” says Carroll,  ”the big concern for AC devices is loss in dielectric. Nano particles make it tremendously non-lossy.”

 

The polymer mix has three different emission centres coupled with triplet scavengers, says Carroll: “You get singlets and triplets and the triplets are non-radiative. Normally OLEDs have scavengers too. In our’s, the effectiveness of triplet to singlet conversion is far higher.” 

Its structure is similar to well-established AC electroluminescent technology.

“In AC electroluminescent, light output is around 0.1cd/A. OLED delivers 50cd/A, and ours is 62cd/A,” claims Carroll.

 

This 62cd/A figure is at the very cold colour temperature of 6,800-7,200K, where the technology is likely to be emitting at its most efficient.

 

The polymer mix has three different emission centres coupled with triplet scavengers, says Carroll: “You get singlets and triplets and the triplets are non-radiative. Normally OLEDs have scavengers too. In our’s, the effectiveness of triplet to singlet conversion is far higher.” 

 

Its structure is similar to well-established AC electroluminescent technology.

“In AC electroluminescent, light output is around 0.1cd/A. OLED delivers 50cd/A, and ours is 62cd/A,” claimed Carroll.

 

This 62cd/A figure is at the very cold colour temperature of 6,800-7,200K, where the technology is likely to be emitting at its

Operation is at  ”similar voltage to OLED”,  says Carroll, and efficiency is “certainly comparable with compact fluorescents”.

 

The university has described the technology as “at least twice as efficient as compact fluorescent bulbs and on par with LEDs”.

 

Currently, high-end commercial LEDs are producing around 120lm/W, straight fluorescent tubes can approach 110 lm/W, and good compact fluorescents may approach 80 lm/W. Commercial OLEDs are extremely rare and lab figures would be un-representatively high.

 

The actual emissive layer is 200nm if a polymer called PVK, loaded with 10% of the light-emitting iridium compound Ir(ppy)3, and a fraction of a percent of nanotubes.

This is sandwiched between two 1.2µm layers of the ferroelectric polymer P(VDF-TrFE).

 

The nanotubes both inject electrons and generate charges, said Carroll, and the same structure without nanotubes produces only one fifth of the light.

 

The spectrum can be tuned to different colour temperatures. “It is a continuous spectrum. We can almost make a perfect photopic curve,” said Carroll.

 

Matching the eye’s response – the photopic curve – would mean poor rendering of red and purple. Can he match the sun’s spectrum instead?

 

“Yes, we can make the sun’s spectrum,” said Carroll.

 

The big problem for OLEDs is durability – water and oxygen from the atmosphere corrode the necessarily reactive electrodes and the organic materials involved.

 

There are no reactive metal electrodes in the FIPEL structure. “If a triplet hangs around, it will oxidise the material,” said Carroll. “We have the shortest life of any triplets – so longer material life and much longer lifetime.”

 

How about moisture and oxygen? “For our device to reach 20,000 hours, they still have to be encapsulated, but they are not so sensitive as OLEDs,” responds Carroll, “if you use expensive encapsulation, you will get 40,000-50,000 hours.”

Tags: colour temperature, layers of light, light emitting polymer, nano particles, triplet

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11 Comments

  1. Sub Editor
    December 11, 2012 16:32

    Paragraphs 6 to 8 are repeated in paras 9-11.
    200nm of a polymer not if
    Very interesting anyway…
    Mike

  2. David Manners
    December 10, 2012 20:25

    Personally, Aristotle, I think ARM’s small ‘take’ is a positive. It is offering a world standard (which is always useful) without setting up a business model whereby it can become hugely rich and powerful as a result. We have seen what happens when a company does get hugely rich and powerful by owning a world standard – and it’s not a pretty sight. As for Plessey you’re right it’s a fantastic initiative. A really good thing to see happening here. I think we all wish them the greatest success.

  3. David Manners
    December 10, 2012 20:17

    That’s a great quote, Stooriefit, thanks But remember what happened when the Luftwaffe General and fighter pilot ace Adolf Galland was asked by Goering what he needed during the Battle of Britain, and Galland replied: “A squadron of Spitfires” whereupon Goering, according to Galland: “Stamped off growling as he went.”

  4. Stooriefit
    December 10, 2012 13:06

    One of the best endorsements for British Technology comes from an unexpected source:
    “In 1940 I could at least fly as far as Glasgow in most of my aircraft, but not now! It makes me furious when I see the Mosquito. I turn green and yellow with envy. The British, who can afford aluminium better than we can, knock together a beautiful wooden aircraft that every piano factory over there is building, and they give it a speed which they have now increased yet again. What do you make of that? There is nothing the British do not have. They have the geniuses and we have the nincompoops. After the war is over I’m going to buy a British radio set – then at least I’ll own something that has always worked.
    — Hermann Göring, 1943″
    Which is from the wikipedia page on the De Havilland Mosqueto.

  5. Aristotle
    December 09, 2012 05:58

    While ARMH is indeed British only a tiny fraction of ARM SOC revenue lands within these shores. The products re designed and marketed by someone else … and the manufacturing executed by a third party. UK plc can only claim a small slice.
    It will indeed be a laudable success if Plessey can pull off the IDM thing wholly inside dear old Blighty. Good luck lads!

  6. David Manners
    December 06, 2012 20:41

    Oh I don’t think so, Anonymous, we came third in the Olympics, won the Tour de France, have our own currency, are No.1 for soft power on the planet and have the world standard mobile processor – being British these days is the best thing out.

  7. Anonymous
    December 06, 2012 18:35

    … and it’s British !
    Oh that’s regarded as a negative nowadays. Oh well.

  8. David Manners
    December 06, 2012 16:43

    I think you use a Plessey GaN on silicon offering 160lm/W [Anonymous] because it will certainly arrive sooner, will probably be cheaper and undoubtedly has a better intellectual provenance.

  9. David Manners
    December 06, 2012 16:39

    .. Not yet revealed Anonymous, but will, be published shortly, in Organic Electronics http://www.sciencedirect.com/science/articles/pii/S1566. 2. Don’t know.

  10. Anonymous
    December 06, 2012 14:42

    1. What is the projected lm/W?
    2. Would it be variable/ dimmable with conventional dimmer switches?

  11. Anonymous
    December 06, 2012 12:15

    Or you just use a Plessey (or other) GaN on silicon LED giving >160lm/W at lower cost.