Organic light-emitting transistors offer alternative to OLEDs

10 May 2010

A variation on OLED technology developed in Italy opens new opportunities for lighting.

The National Council of Research's Institute of Nanostructured Materials in Bologna, Italy, has created organic light-emitting transistors (OLETs) that integrate both the electric and optoelectric properties of a light-emitting electronic device into a single structure. The result is a technology that offers greater efficiencies than OLEDs.

OLET devices solve the fundamental problems of photon losses and exciton quenching - losses in charge - that are bound up in the structure of OLEDs. OLETs include switching mechanisms, and offer more controlled, surface source light emission.

Michele Muccini, head of the research unit, explains: 'There are limitations for OLED lighting, despite being great devices and near to market. High currents are pushed in that converge on the emissive layer. The way these interact severely degrades the device under high input.'

Surface source

While OLEDs remain the best source for large-area lighting, according to Muccini, OLETs could be used for controlled emission of light on a smaller surface.

Muccini adds: 'OLETs lie somewhere between large-area source lighting for OLEDs, and point source for LEDs. For integrated sources that control the position of light and need more efficiency, OLETs could be used.'

One application is optoelectronic biosensors, where an analyte that detects disease markers is activated by a light. The research is feeding into an EU-funded project, called Photo-FET, to develop such a biosensing device, integrating an OLET light source into a microfluidic chip. Muccini is coordinating the project to integrate photonic, field-effect technology for bio-sensing functional components, working with a consortium that includes UK-based point-of-care device developer Molecular Vision and material science firm SAES Getters in Italy.

The €4 million project began earlier in 2010 and will produce a demonstrator of a biosensing device for the end of the initiative by the end of 2012. This will include the use of an OLET to excite the analyte in a controlled manner.

Manufacture

Muccini's research group must bring down the voltage required to power OLETs, and improvements in this area are expected soon.

Once more acceptable operational voltages are achieved, OLETs could be used in real applications, and the research group is in contact with manufacturers about preparing the supply of OLETs.

'OLETs are of interest for industrial devices, and we're considering the technology push with some European partners. Applications will follow once we develop the technology base [for supply of OLETs], and biosensors is one of these,' Muccini adds.

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