First author

When it comes to buying light bulbs, consumer choice is pretty limited. Incandescent bulbs, the most popular option, are widely available and inexpensive, but most of the energy they produce is given off not as light but as heat. Green-minded consumers favour the much more efficient compact fluorescent lamps (CFLs), but CFLs typically cast a colder, less attractive light and, because they contain mercury, are difficult to dispose of. Several groups have thus been working on better alternatives. One option, under study by PhD student Sebastian Reineke and his colleagues at the Institute for Applied Photophysics in Dresden, Germany, is organic light-emitting diodes (OLEDs), thin films of organic molecules that emit light when current passes through them. Until now, their drawbacks have included their comparably low efficiency, but Reineke's team has hit on a solution (see page 234). He tells Nature more.

What inspired this work?

Trying to find solutions that save energy has been one of the driving forces of our research. OLEDs had already been shown to have the potential to become one of the next-generation light sources. We are now in global competition to accelerate the commercialization of white OLEDs.

What is the benchmark for energy efficiency?

CFLs provide 60–70 lumens per watt — the ratio of light produced to electricity used — compared with the 15 lumens per watt produced by the average 60-watt incandescent bulb. We have now achieved OLEDs that produce 90 lumens per watt and emit soft area light.

Were there any surprises?

OLEDs emit light as electrical current flows through their organic layers, with the colour of the light depending on the type and number of organic dyes used. But most OLEDs show a shift in colour when the strength of the current passing through them changes — an unwanted feature for dimmable light sources. We were surprised to discover no such colour shift in our OLEDs, no matter how much current we passed through them.

What do you see as future uses for OLEDs?

OLEDs are ultrathin devices that can be scaled to almost any size. You could use one as wallpaper — it would be a thin sheet emitting soft, comfortable light. Or it could be part of a window, where the organic layers — a few hundred nanometres thick, and invisible to the naked eye — are set between layers of glass. During the day it would just look like a window; at night you could turn it on and it would emit light.