What They Say
Scientists at the University of Utah and the NREL have developed a new LED that is said to use spintronics to produce light that is circularly polarised. The LEDs do not need a magnetic field, magnetic materials or cryogenic temperatures to achieve light emission as spin-polarised carrier pairs. The research was published in “Science, Vol 371 issue 6534 pp 1129-1133”
The abstract in Science said:
“In traditional optoelectronic approaches, control over spin, charge, and light requires the use of both electrical and magnetic fields. In a spin-polarized light-emitting diode (spin-LED), charges are injected, and circularly polarized light is emitted from spin-polarized carrier pairs. Typically, the injection of carriers occurs with the application of an electric field, whereas spin polarization can be achieved using an applied magnetic field or polarized ferromagnetic contacts. We used chiral-induced spin selectivity (CISS) to produce spin-polarized carriers and demonstrate a spin-LED that operates at room temperature without magnetic fields or ferromagnetic contacts. The CISS layer consists of oriented, self-assembled small chiral molecules within a layered organic-inorganic metal-halide hybrid semiconductor framework. The spin-LED achieves ±2.6% circularly polarized electroluminescence at room temperature.”
“The companies that make LEDs or TV and computer displays don’t want to deal with magnetic fields and magnetic materials. It’s heavy and expensive to do it,”
“I’d love that someone will come out with another 2-D organic/inorganic layer material that may do a similar thing. At this stage, it’s very general. I’m sure that with time, someone will find a different two-dimensional chiral material that will be even more efficient,”
said Valy Vardeny, distinguished professor of physics and astronomy at the University of Utah.
What We Think
This is R&D and the level of emission is small, but there is a lot of work going on in this area at the moment. As well as the Science article, there is a release by the University of Utah here. (BR)
From bottom to top. The first layer is a semitransparent anode, such as ITO, that injects unpolarized “holes,” a quantum feature of electrons, with a certain spin. The second layer is the two-dimensional chiral hybrid perovskite that is an active spin filter, allowing only holes with specific spin to pass by, depending on the helicity of the chiral molecules. The third layer is the emitter film, composed of a non-chiral inorganic perovskite such as CsPbBr3. The fourth and fifth layers are the cathode that injects spin up and spin down electrons. Only the spin down electrons recombine with the spin up injected holes to produce circularly polarized light with helicity that depends on the chiral molecules helicity in the two-dimensional organic-inorganic layer. Click for higher resolution
