UV OLED can be used as an on-chip photosensor
04 October 2015
Ames Laboratory in the US has developed a near ultra-violet and all-organic light emitting diode (OLED) that can be used as an on-chip photosensor.
The development is a first in a rather specialised field of research to capture and manipulate light near the invisible end of the spectrum - around 400nm wavelength.
“The real pie in the sky goal is a tiny chip that is a whole spectrometer, so it can measure the absorption or luminescence spectrum of anything that can absorb or emit light," says Ames Laboratory scientist Joseph Shinar. "This is a step in that direction.”
While there has been high interest in visible OLEDs as alternatives to conventional LEDs in widely-used applications such as consumer electronics, there has been much less investigation into OLEDs in the ultra-violet spectrum.
“And that has failed to address a rising demand of small-size, flexible devices for analytical applications,” says Ames Laboratory associate Ruth Shinar, a scientist at Iowa State University’s Microelectronics Research Centre.
“Such devices can be used for detection in food safety, water quality, medical diagnosis and other fields where biosensing is necessary," she says. "They can be hand-held, used in the field, and potentially inexpensive and disposable.”
The researchers’ work exploits the effects of optical microcavities, which are structures formed by the reflective surfaces on either side of an optical medium. The small size of microcavities alters the behaviour of light wavelengths.
These altered characteristics allow UV OLEDs with narrower emission spectra to be tuned to specific wavelength emissions for sensing and optical excitation. When an array of such OLEDs is created, multiple analyses and optical excitations can be performed on the same device.
Building on previous Ames Laboratory microcavity OLED research, the researchers created a device that could emit light in the wavelength range of 370 to 430nm, the deep blue and near-ultra violet, expanding previous developments in the visible range. They extended the range to 470nm by using a novel combination of two photoactive polymers, CBP and PVK. Combined with an earlier study on visible microcavity OLED arrays, they can now cover the 370 to 640 nm range.
The work is published in the journal, Organic Electronics.