0rganic light emitting diodes capture the market

Paul Boughton

Organic light emitting diodes are made out of structured, stacked layers (stack) consisting of multiple razor thin layers (typically 10 to 60 nm/layer) of organic semi-conducting small molecules, embedded between conductive electrodes coated on glass or flexible film.

When a voltage is applied to the organic semiconductor materials the electric energy (current) is converted and light of an engineerable wavelength is generated within the organic materials stack (organic solid state).

Both, the development of the organic materials as well as the overall stack have leaped forward tremendously over the last years and OLED devices can achieve high efficiency (low power consumption), excellent color properties as well as long lifetime.

Display manufacturers and end users benefit from outstanding properties such as ultimate high contrast, large viewing angle, rich color saturation and fast switching times. It is obvious that the intrinsic benefits of organic light emitting materials captivate the display industry but the future promise goes far above this in multiple industries and applications.

Merck offers under the brand name livilux a complete portfolio of premium materials for OLED displays and OLED light sources. This includes small molecules for vacuum processing, as well as soluble materials for printing processes. With more than ten years experience in development and manufacturing of OLED materials coupled with a strong portfolio of global patents Merck has a solid basis to provide high purity and stable materials tailored to meet commercial requirements.[Page Break]

Merck, as a OLED material developer and manufacturer understands that the device manufacturing industry needs constant innovation to improve, simplify and optimize the production process of OLED products. Let us explore this a little more into detail.

The underneath diagram explains the basic functioning of an OLED device. The transport layers on the electrodes provide the optimal electron and hole injection into the device from respective electrodes. The emitting layers are engineered to have a bandwidth to generate light of a specific wavelength.

The combination in a stack of different emitting materials can generate the different RGB (Red, Green, Blue) primary colors for a display or also alternatively mixing colors such that a white light is emitted. Currently almost all commercially available devices are produced in vacuum vapor deposition chambers (heating of the organic materials will cause them to evaporate). Whilst vapor deposition processes are commonly used in different industries and applications, the big challenge in OLED is to do these processes on a large size and with the needed accuracy for high production yield.

Specifically for large display such as TV, where the so called mother substrate has a size of over 9 square meters, this process proves to be very difficult and costly. To scale up OLED, the production process issues have to be tackled and process simplification is needed.[Page Break]

Already years ago, the question was raised: would it be possible to print OLED on a large scale?

Obviously the above is in analogy with the paper printing industry where large size and fast printing processes have been established since long time.

Research institutes and companies alike have long pondered and worked to find an answer to the above question. Different solutions have been proposed but so far most failed to achieve reasonable performance and lifetime that is needed for commercial viability. One major hurdle was, OLED materials need to be soluble to be used in a printing process.

Merck has diligently worked on the subject and also lead a German government project (BMBF, NEMO) to really go to the bottom of the issue, defining obstacles and solving roadblocks. One major learning was simply based on the acknowledgement of “if it works don`t change it”, meaning in this case, using the evaporable small molecule that are applied in current OLED products and chemically re engineer them for usage as soluble material.

The Merck chemists developed a tool box to change a functioning small molecule such that it becomes soluble without changing any of its electro optical properties.

Having addressed this issue, Merck now is working together with innovative and experienced printing process suppliers to study and improve the applicability of soluble materials in different state of the art printing processes.

This forces us to address and propose solutions for diverse printing related issues such as ink rheology, film building, phase separation, viscosity etc.

Also here Merck, together with process partners, is well on its way to successfully tackle issues and the progress & result in the recent years, give us a high level of confidence printing displays and lighting devices on a large scale will soon be possible and the future holds may fold new applications.

Watching the development of this exiting OLED technology seems worthwhile.

For more information, www.merck-performance-materials.com.

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