The First Spin OLED: A Giant Step towards a New Light

What is the coolest thing about the strides made in producing a spin-polarized, light-emitting diode (spin OLED)? Efficiency: spin OLEDs can theoretically produce twice as much light for the same power consumption and generate a range of colors from a single diode.

Organic spin valves consist of an organic spacer layer sandwiched between two spin-polarized ferromagnetic electrodes (one of cobalt, the other of  lanthanum strontium manganese oxide). Modifying them to emit light as an LED does--opening the door to a more energy efficient light source--has seemed the natural extension of the technique since it was first demonstrated in 2004. Until now, though, the technical details have frustrated researchers.

In the July 13 issue of Science, physicists Z. Valy Vardeny, Tho Nguyen, and Eitan Ehrenfreund showed how to make a spin OLED work. The stride was actually more of a two-step: 

First, they replaced the material of the first demonstrated spacer layer--aluminum tris(8-hydroxyquinoline), or Alq3--with a new organic polymer, deuterated poly(dioctyloxy)phenyl vinylene (D-DOO-PPV for short). D-DOO-PPV is a π-conjugated polymer; replacing hydrogen atoms near the molecular backbone with deuterium increases light-emission efficiency.

Second, they modified the cobalt electrode, applying a lithium fluoride monolayer. As Vardeny describes it, this allows negatively charged electrons to be injected into the gate on one side of the valve while positive positron “holes” are injected through the other side. 

The authors frankly acknowledge that there's still a lot of work to do on the 300 μm x 300 μm x  40 nm prototype (photo at left) before spin OLEDs become everyday commodities. The current model works only in the cold: Output starts to fall off around 200 K (-73 C) and stops at about 240 K (-33 C). And the prototype emits only a single (orange) wavelength, though in theory many colors are possible.

Photo: Tho D. Nguyen, University of Utah. 


Tech Talk

IEEE Spectrum’s general technology blog, featuring news, analysis, and opinions about engineering, consumer electronics, and technology and society, from the editorial staff and freelance contributors.

Newsletter Sign Up

Sign up for the Tech Alert newsletter and receive ground-breaking technology and science news from IEEE Spectrum every Thursday.