Improving the quality of displays

High-speed , reproducible and reliable processes, such as roll-to-roll display manufacturing is proving effective in the fabrication of light-emitting polymers (LEPs).

By using inkjet printing and the silk screening of organic materials, LEPs are able to reduce manufacturing cost through effective material use.

"LEPs offer all the advantages of small-molecule technology such as low power consumption and low power consumption and low drive voltages," says Technical Insights analyst Joe Constance. "LEP devices can generate sharp light output and can be fabricated cost-effectively in high-pixel density configurations," he adds.

Efficient control over structural order in LEPs is required to have an edge over traditional LCDs. In this regard, polymers that have different band gaps may prove to be a key factor in outplaying competing technologies.

Emission of red, green or blue light is possible with different bands, making full-colour displays with conductive LEPs commercially viable. Intense research in this area has enabled poly-phenylene vinylene (PPV) to emit blue light by interrupting conjugation in the polymer with non-conjugated units. Attachment of alkoxy side groups to the phenylene rings of the PPV enable red light production.

A full-colour polymer-based display required pixellating the colours through the combination of different conducting polymers with varying band gaps. The colour emitted from the blend will depend on the amount of voltage applied, which increases with the band gap.

An alternative route would be to use white-light emitting diodes to create a micro-cavity, the length of which determines the colour of the emitted light.

Apart from varying band gaps, polymer-based light emitting diodes also face the challenge of increasing operating lifetimes to at least 20,000 hours to popularise commercial usage. When the luminance intensity of the device decreases to 70% of the original value, it is considered the actual end of life as opposed to 50% referenced for display applications.

"In the area of LEPs, significant research has been in progress to improve material lifetimes both through the use of materials that are resistant to oxidation and through improved encapsulation," explains Constance.

Conducting polymers based on doped polyaniline, conjugated polymer material and polypyrrole are already demonstrating the stability required for commercial applications, proving the potential for growth and wider acceptance in the future.

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