Challenges In OLED Research and Development III: Solution-Based Materials

Solution based materials are a different way of processing the conventional OLED materials. So conventional OLED materials are processed by vacuum thermal deposition or heating up a powder in a crucible and evaporating it onto the substrate. Solution process materials are dissolved in a variety of solvents and then they can be coated by spin coating for lab sized experiments, or ink-jet printing, or slot-die coating, or a variety of other printing methods.

Solution based materials can give you some advantages in manufacturing. It could be a little bit easier to apply. They're easier to handle and they can bring the cost down. Printing equipment is conventionally used in a lot of processes. And the substrate could come in a roll and have continuous processing and this tends to be a slightly cheaper method of manufacturing than a sheet to sheet method that is what's being done today with vacuum thermal deposition.

(The Office of Energy Efficiency & Renewable Energy/ LEDinside)

Solution based materials are quite challenging. One, because most of the materials used in OLED today are not remarkably soluble. A lot of them are really rocks. So finding a solvent to put them in is quite difficult. And also a solvent that doesn't degrade the electro-optical properties of the material over time that can be very stable. Once you make an ink, you want to be able to ship it to the manufacturer and have it sit on their shelf also for a few months and still give the same results from printing. So there's a lot of work going on today about finding the right solvents that are shelf stable that keep the properties but also dissolve these very rock like materials.

And consequently, the DOE has also developed new materials that are analogous to what the DOE uses for vapor but are slightly more soluble. So it keeps the electo-optical core but it puts some different moieties around to make it more soluble. So there's a lot of optimization that goes on with those materials as well. The DOE is believed to really start to see solution processing of OLED displays in the next one or two years with mass production shortly thereafter. For lighting it's a little bit more of a challenge because it does not need to make very fine pixels of RGB for lighting. It's really a uniform white color. So there hasn't been a manufacturing push but once it becomes established in display, and those materials are more ubiquitous, and more available, and the cost comes down, those will be more available and attractive to lighting manufacturers as well. 


(Source of knowledge: The Office of Energy Efficiency & Renewable Energy, U.S.)

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