Organic light-emitting diodes (OLEDs) that use the principles of ‘spintronics’ could be brighter, cheaper and more efficient than standard OLEDs, according to a US team investigating the idea.
‘It’s a completely different technology,’ said Valy Vardeny of Utah University who has created a prototype spin-polarised OLED that produces an orange colour operating at -33ºC.
The latest work was actually made possible by another device called an organic spin valve.
These are essentially electrical switches — found in computers, TVs and mobile phones — that use a property of electrons called spin to transmit information. Spin is defined as the intrinsic angular momentum of a particle where up and down can correlate to the zeroes and ones in binary code.
Organic spin valves are composed of three layers: an organic layer that acts as a semiconductor sandwiched between two metal electrodes that are ferromagnets.
A low voltage is used to inject negatively charged electrons and positively charged electron holes through the organic semiconductor. When a magnetic field is applied to the electrodes, the spins of the electrons and electron holes in the organic semiconductor can be manipulated to align either parallel or antiparallel.
In the current new study, the crucial advances in the materials was to create ‘bipolar’ organic spin valves that allow the new spin OLED to generate light, rather than just regulate electrical current.
It is the ability to inject electrons and holes at the same time that allows light to be generated. When an electron combines with a hole, the two cancel each other out and energy is released in the form of light.
The intensity of the new spintronic OLEDs can be a controlled with a magnetic field, while older kinds require more electrical current to boost light intensity.
Also, existing OLEDs each produce a particular colour of light — such as red, green and blue — based on the semiconductor used. According to Vardeny, in the spin OLEDs, a single device could in theory produce different colours when controlled by changes in magnetic field.
The next challenge, though, will be to get the technology working at room temperature.