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OLET May Render OLED Obsolete

by May 07, 2010
May not mean anything now, but one day your eyes may appreciate it.

May not mean anything now, but one day your eyes may appreciate it.

Still holding out on plopping down two grand for a sweet 11” OLED?

Worried about the pace of OLED development now that major commercial players like Sony are dropping out of the picture?

Get ready to keep holding your breath for a new hope: the Organic Light Emitting Transistor (OLET).  As noted on Nano Werk via Engadget, recent research published in Nature Materials by a group of scientists at the Institute of Nanostructured Materials (ISMN) in Bologna, Italy and Polyera Corporation in Skokie IL, details significant improvements that have been made to current OLET design.

The paper, Organic light-emitting transistors with an efficiency that outperforms the equivalent light-emitting diodes details findings that suggests OLET can outperform OLED in both brightness and efficiency in emitting light, a problem that is central to continuing OLED development.  From the abstract:

The potential of organic semiconductor-based devices for light generation is demonstrated by the commercialization of display technologies based on organic light-emitting diodes (OLEDs). Nonetheless, exciton quenching and photon loss processes still limit OLED efficiency and brightness. Organic light-emitting transistors (OLETs) are alternative light sources combining, in the same architecture, the switching mechanism of a thin-film transistor and an electroluminescent device. Thus, OLETs could open a new era in organic optoelectronics and serve as testbeds to address general fundamental optoelectronic and photonic issues. Here, we introduce the concept of using a p-channel/emitter/n-channel trilayer semiconducting heterostructure in OLETs, providing a new approach to markedly improve OLET performance and address these open questions. In this architecture, exciton–charge annihilation and electrode photon losses are prevented. Our devices are >100 times more efficient than the equivalent OLED, >2× more efficient than the optimized OLED with the same emitting layer and >10 times more efficient than any other reported OLETs.

The basic structure of an OLED is to sandwich an organic emissive and a conductive layer of materials between an anode and a cathode on a substrate.  Light is generated by applying voltage across the OLED to create electron flow from cathode to anode, which produces electron holes in the conductor as the emissive layer builds up negative charge.  As the two layers seek to rebalance charge at their boundary, photons are given off.

On the other hand, the OLET structure that the researcher developed uses a three-layer organic field effect transistor (FET) structure.  The structure consists of a hole-transporting (p-type) layer, a light emitting middle layer, and an electron-transporting (n-type) layer on a Poly methyl methacrylate (PMMA) dielectric layer, and an indium tin oxide (ITO) gate layer deposited on a glass substrate.  By providing better control over the electrical fields, this structure allowed a double order of magnitude increase to efficiency in producing light when compared with using the same organic electro luminescent materials in an OLED configuration.

But Will It Blend?

Like OLED, the researcher claim that the OLET structure can be applied to a range of substrates using common microelectronic methods.  Possible substrate materials include silicon, glass, plastic, and paper allowing for a wide range of possible uses, not only for display technology but for optoelectronic applications like optical switching on microchips.

Obviously, there is still work to be done in the lab at this point, but OLET does provide a very interesting potential alternative to OLED, which is not exactly ready for consumer primetime either, as evidenced by the $2000-a-pop mini OLED screens for sale.

About the author:
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Professionally, David engineers building structures. He is also a musician and audio enthusiast. David gives his perspective about loudspeakers and complex audio topics from his mechanical engineering and HAA Certified Level I training.

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