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OLED technology: introduction and basics

What is the OLED technology all about?

OLED panels are made from organic (carbon based) materials that emit light when electricity is applied through them. Since OLEDs do not require a backlight and filters (unlike LCD displays), they are more efficient, simpler to make, and much thinner. OLEDs have a great picture quality - brilliant colors, fast response rate and a wide viewing angle. OLEDs can also be used to make OLED lighting - thin, efficient and without any bad metals.

Continental flexible AMOLED based car display prototype

OLED materials have been discovered back in 1960, but only in the past 20 years or so have researchers started to actually work on the technology. A complete history of OLEDs can be found here. You can read more about OLED displays and advantages in our OLED introduction page.



How do OLEDs work?

The basic structure of an OLED is a cathode (which injects electrons), an emissive layer and an anode (which removes electrons). Modern OLED devices use many more layers in order to make them more efficient, but the basic functionality remains the same.

How an OLED panel is made

Making an OLED involves several steps: taking a substrate, cleaning it, making the backplane (the switching and driving circuitry), depositing and patterning the organic layers and finally encapsulation the whole thing to prevent dust, oxygen and moisture damage.

There are several ways to deposit and pattern the organic layers. Currently most OLED displays are made using vacuum evaporation, using a Shadow Mask (FMM, Fine Metal Mask) to pattern. This is a relatively simple method but it is inefficient and very difficult to scale up to large substrates. There are several alternatives - mostly using soluble OLED materials that are deposited using printing methods. OLED makers hope that these processes will prove to be more scalable and more efficient than vacuum deposition processes.

OLED materials

There are several types of OLED materials. The most basic division is between small-molecule OLEDs and large molecule ones (called Polymer OLEDs, or P-OLEDs). All commercial OLEDs today are SM-OLED based. These evaporable materials perform better han P-OLED materials (in terms of efficiency, lifetime, etc.). P-OLEDs had great promise as they are naturally solution processable (and so can be used in InkJet printing and spin-coating fabrication methods). Intensive research is being performed to develop efficient solution-processable SM-OLEDs.

OLED emitter materials are classified as either fluorescent or phosphorescent. Fluorescent materials last longer but are much less efficient than phosphorescent materials. Currently most OLED displays use phosphorescent emitter materials - except for the blue color which is still fluorescent as the lifetime is still not good enough. Universal Display Corporation is pioneering PHOLED research, holding the basic patents in this area.

AMOLED vs PMOLED

These terms relate to the driving method of the OLED display. A PMOLED (Passive-Matrix OLED) is limited in size and resolution, but is cheaper and easier to make compared to an AMOLED (which uses an Active-Matrix). An AMOLED uses an active-matrix TFT array and storage capacitors. While these displays are more efficient and can be made large, they are also more complicated to make.

PMOLED displays are used in small devices or secondary displays while AMOLEDs are used in smartphones, tablets and TVs. Here's more information about the difference between PMOLED and AMOLED.

Challenges

The are still many challenges facing the OLED industry. Here's a list of some of the major ones:

  • Material lifetime (especially of the blue material)
  • Soluble OLED performance
  • Soluble-based production processes
  • Flexible OLED encapsulation
  • Better backplane materials for flexible OLED
  • Scaling of evaporation processes beyond Gen-6
  • OLED lighting capacity expansion

OLED technology today

The leading AMOLED producer today is Samsung, who's making over 200 million displays a year, and is still expanding production capacity. Samsung is focused on small displays (5 - 10 inch) mostly for mobile phones and tablets. LG Display is also producing OLEDs, but only large size (55-77 inch) panels for OLED TV applications. You can see a list of gadgets with OLEDs here.

Samsung GS6 and GS6 Edge photo

Both Samsung and LG also produce flexible OLED panels, used in mobile phones and wearable devices. Production volume is still rather low, but both companies are expected to expand production capacity and introduce new products and form factors to the market.

In the OLED lighting market, several companies (including as Philips, LG Chem, OSRAM and Konica Minolta) are already shipping OLED panels, but production capacity is still low and prices are very high. OLED lighting today is mostly used in premium lighting fixtures and installations.

LG Chem truly flexible OLED lighting panel photo

Further reading

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