What is holding back OLEDs?

What is keeping Organic Light Emitting Diodes from our laptops and PDAs? They are already being used in some small devices like phones, and car stereos, why not other devices. I thought that OLEDs where better than regula LED displays in every way, a thousand times faster, far lower energy requirment (no backlight needed).

So where are they?

I don’t know, but I want OLED tv!!! You forgot that they’re super-thin and super-flexible too!

According to this site, they are very susceptible to atmospheric moisture.

Why is it better?

OLEDS are better than normal LEDs for a number or reasons… They are considered simpler to manufactuer to begin with, and on top of that, they create enough light on thier own so they they do not require backlighting.

They can be produced on flexible backing. There has even been talk about them eventually being woven into clothing.

And recently, there was a very startling discovery. You see with normal LEDs, one LED makes one color. To create an LED display, you need lots of LED arranged in pixel. Each pixel is actually composed of 3 LED sub pixels (a red, green and blue). SInce each pixel has to be controlled indivdually to create images on your LED screen, there is wiring to each LED, making for one complicated peice of equipment.

But there was an accidental discovery, and this was literally only a few weeks back, of a OLED that was able to change color depending on the charge it was provided. Currently, i think it can change from green to blue. Now that it is known that OLEDs have this ability, additional research will be done to create OLEDS that can, depending on charge, create RGB. Once this has been accomplished, OLEDS displays can be created that will only require a 3rd of the complexity of existing displays, since 1 OLED pixel can handle Red, Green and Blue tasks. (alternatively, we might just see displays with triple the resolution)

OLEDs are a bit fragile currently (they are very new technology) sensitve to moisture, and they dont have as long of life as current LEDs. But once they are able to make them last longer, and once color changing OLEDs are available, flat panel displays will be much cheaper, and more plentiful.

There was an interesting scene in the movie Minority Report where Tom Cruise picks up a box of cereal and the back of the box is animated like a TV screen. It may very well be possible by that time frame that OLEDs will be cheap and plentiful enough to make using them as cereal boxes would be completely cost effective (I always find that mind boggling)

bcullman: A lot of the really neat microminiaturization is held up by century-old battery technology: The best thing we currently have to store power for small devices are basically the same dry cells we’ve used for decades now, in slightly different shapes but nothing radically different. Quite frankly, you can have OLEDs growing on trees and it won’t do you a bit of good for making cereal boxes unless you’re willing to invest massively in power storage (or, alternatively, microgenerators of some type).

Of course, revolutionary power storage systems would solve problems of all types, from electric cars to practical robots.

It may not be a huge problem, since OLED displays are fare more energy-efficient than LCD displayus. Roughly speaking, an OLED display should have less than 1/6 the power consumption of a color LCD display. On a backlit LCD panel, the polarizing filter which is part of the LCD panel blocks half the light. On a color LCD panel, the color filter on each pixel absorbs an average of 2/3 of the remaining light. (Blue filter absorbs green and red, green filter absorbs red and blue, etc.) In addition, the entire LCD must be backlit all the time even when displaying a mostly black screen. An OLED screen can selectively turn on individual light-emitting pixels so there is no wasted light.

OK, so maybe a small battery is still too expensive to include in a cereal box, but maybe if they could develop organic solar cells that can be fabricated on the same substrate…

LEDs doesn’t need backlighting, LCD does.

LEDs are very simple to make already, pretty much just a diode with a couple of extra steps. Which is piece of cake with the pretty mature technology we have for making ICs.

LEDs are made of AlGaAs, InGaN and other semiconductors. IIRC the fabrication technique for these are very different from silicon chips.

You can make LEDs from all sorts of semiconductor materials, including GaN and even silicon. There are certain differences, but it has been like two decades since we can make GaAs ICs, it’s a cakewalk really.

Not really. Think about it. You need enough battery power to supply the OLED with juice for maybe twenty minutes a day for a week. That’s less than 2.5 hours. I don’t find it implausible at all that batteries will become cheap enough, in the next couple of decades, to make such a wasteful product feasible… especially if you look at how much cheaper batteries have become in the past two or three decades.

you happened to pick my post-doc research area so…

OLEDS come in two types - sublimed small molecules and solution based polymer types. The first are hard to make quickly, so not so good for large scale manufacture. The japanese have gone down this path mainly. The second is being developed rapidly by a number of companies.

However, LCDs have had a huge head start. To make a factory making large scale displays will probably cost up to a billion, so everything must be perfect. Several things holding back OLEDs

operating lifetimes: in practice not always good enough for a display (20,000 hours needed). But for cell-phones or other consumer products it is fine. Currently can get reliably between 1000-10,000 hours depending on colour and type.
Addressing: To get a large display you need active matrix addressing, e.g silicon backplane. Not cheap on a large area, and back-planes have so far only been optimised for LCD displays (e.g. voltage driven) rather than OLEDS (current driven). The OLEDs also drift a little during operation, so need compensation circuitry. All quite possible, but that is another factory again to make the backplane.

Efficiency. At the moment a little bit better, but not 6 X as good as LCDs. The problem is that the OLEDs have lots of small losses that also add up, e.g. higher than wanted voltage operation, less than 100% fluorescence efficiency, less than 100% charge capture, less than 100% colour purity. The main advantage of OLEDs is their wide viewing angle and much faster refresh rate. They should also be be more efficient, but only in an ideal world. See CDTs website for more details www.cdtltd.co.uk/

Competing technologies
OLEDs will have to battle it out against ferroelectric LCDs (fast and good viewing angle, known technology), plasma displays, field effect displays etc. No one is going to commit a billion pounds yet, so we will have to wait a few years until they prove themselves, and gradually expand their market. Of course by then other technologies may have come through. e.g see http://www.screentechnology.com/tech/

The hype about flexible OLEDs on clothing etc may be a long way off. These displays are very very sensitive to oxygen and water during operation and need outstanding encapsulation. they are also very sensitive to variations in thickness, and so are not suited to coating on rough surfaces. On the other hand, WRONZ ( http://www.wronz.org.nz/wronz-main/index.shtm )has developed an inorganic variety that can go through the wash! Sorry cant find a direct cite, but I have held it in my hand so it must be true.

only cite I could find on light emmiting fabric is http://www.e-insite.net/semiconductor/index.asp?layout=article&articleid=CA193562 which is being developed by softswitch ltd

Looks like someone may have gotten around the water and oxeygen problem

Small monochrome OLEDs are becoming fairly common in phones, MP3 players and the like. Even with though the displays are small, the yields are still fairly low. Just one bad pixel out of 10,000 and the display is scrap. In order to make something very large like a computer monitor or a TV screen, it would take many hundreds if not thousands of displays to get one to pass. That computer monitor would end up costing tens of thousands of dollars.

Haj

Why would the entire screen fail if a single element failed?