Hullabaloo about OLED

It's been a long time coming, but it seems that OLED displays are finally beginning to creep onto the market.

It's been a long time coming, but it seems that OLED displays are finally beginning to creep onto the market.

It's easy to understand why people are excited about this new display technology. It's more energy efficient, brighter and crisp at any viewing angle. It can also be made into flexible displays, has contrast ratios of up to 1,000,000:1, and is potentially much cheaper to produce than current LCD technology.

The concept behind OLED is fairly simple, rather than using polarised molecules to block backlighting (LCD), or the elemental emission of superheated noble gases (plasma), OLED uses the electroluminescence of organic compounds. Thus the name, organic light emitting diodes (OLEDs).

A subgroup of this technology is polymer light emitting diodes (PLEDs), which use the electroluminescence of conjugated organic polymers (which act as semiconductors). Semi-conducting organic polymers are a big deal; they have big implications for molecular electronics, which is perhaps why the guys who discovered them received a Nobel Prize.

In PLED, different polymers are used to produce different wavelengths, so different polymers are used for red, green and blue. Simple polymers like Poly(p-phenylene) (a polymer of benzene) can be used to produce blue, but as we move up wavelengths towards green and eventually red, more complicated polymers are needed.

These polymers are then sandwiched between an anode and a cathode in a matrix of tiny cells (each containing a red, green and blue polymer diode), and fixed onto a substrate (typically glass). This forms an OLED pixel. As these polymers can be dissolved in an appropriate solvent, they can be 'printed' directly onto a substrate, creating the low production cost.

Printed polymers also mean flexible displays, finally bringing the dream of true, flexible digital paper to life. I haven't heard of any commercial uses for flexible displays yet, but what I have heard of is use of the technology on small electronic devices and televisions.

Despite the unbelievable promise of this technology, there are a couple of catches. Firstly, when it comes to light emission, organic polymers just don't last as long as their more stable inorganic rivals, namely LCD and plasma. Figures vary depending on technology, but popular OLED polymers have about one quarter of the lifetime and an LCD display. Polymer impurities will also reduce conductance and conjugation, thus reducing efficiency and luminescence.

Oh, did I mention that they can be 3mm in depth or thinner? They also have response times of less that a one hundredth of a millisecond, well beyond human perception.

Despite all this, there isn't a lot of commercial noise around OLED, the marketing hullabaloo is yet to start. Economies of scale and existing infrastructure mean that vendors will want to get the maximum life and value out of their existing LCD and plasma production processes. Maybe that's why the 11-inch XEL-1 OLED TV is worth US$2,500.

However it's only a matter of time before continued refinement or the creation of novel new polymers brings OLED up to the same lifetime as plasma or LCD displays. This means the future will be sharper and brighter.


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