Screens set to go green

Aug 22, 2011
The molecular structure of the bulky organic ligand that turns copper (green) into an efficient light emitter (yellow, phosphorus; red, bromine). Copyright : © 2011 Masahisa Osawa

Fitting the screens of electronic devices, such as televisions and smartphones, with a new display technology called 'organic light-emitting diodes' (OLEDs) will reduce their energy consumption, but such screens currently require rare and expensive metal components. Now, Masahisa Osawa and his colleagues at the RIKEN Innovation Center in Wako, along with researchers from electronics company Canon, have found a way to replace these costly metals with copper.

In addition to offering significant energy savings over conventional LCD-based displays, OLED screens improve picture quality by producing richer blacks; they also offer a wider viewing angle. In an LCD screen, each pixel is effectively a little filter, selectively blocking light produced by a large backlight. In an , however, each pixel is a tiny light emitter such that no backlight is needed. This means that pixels in dark areas of the image consume no power, reducing energy use.

To maximize the energy-saving benefit, screen makers select OLED materials that most efficiently convert electrical current into light, a property known as high external (EQE). Some of the best materials are phosphorescent , but these are typically composed of rare and expensive metals such as iridium.

Copper complexes have long been known as potential alternatives, and would cost 1/2,000th that of iridium phosphors, according to Osawa. Until the work of Osawa and his colleagues, however, these copper complexes had a low EQE. Such complexes can be readily excited into a high-energy state, but they tend to physically distort, which dissipates their extra energy rather than emitting it as light.

The researchers resolved this problem by altering the molecular environment in which the copper sits. They wrapped each copper ion inside a newly designed bulky organic ligand. They then conducted X-ray diffraction studies, which revealed that the ligand had forced the copper to become three-coordinate—it had formed three bonds to the ligand, rather than the usual four (Fig. 1).

Osawa and colleagues also demonstrated that the EQE of their green-light-emitting copper complex increased dramatically and matched that of iridium complexes. “The three-coordinate structure is a crucial factor for high EQE, because it hardly distorts in the excited state,” Osawa explains.

The team’s next step will be to deploy the complex in a working device. Copper might not be limited to producing green light, Osawa adds. “Our goal is to make red-, green-, and blue-colored phosphorescent three-coordinate materials.”

Explore further: Scientists learn to control reactions with the shape of a rare-earth catalyst

More information: Hashimoto, M., Igawa, S., Yashima, M., Kawata, I., Hoshino, M. & Osawa, M. Highly efficient green organic light-emitting diodes containing luminescent three-coordinate copper(I) complexes. Journal of the American Chemical Society 133, 10348–10351 (2011). pubs.acs.org/doi/abs/10.1021/ja202965y

add to favorites email to friend print save as pdf

Related Stories

Highly efficient organic light-emitting diodes

Aug 09, 2011

(PhysOrg.com) -- Organic light-emitting diodes (OLEDs) are seen as a promising replacement for the liquid-crystal displays (LCDs) used in many flat-screen televisions because they are cheaper to mass-produce. ...

Detecting an unexpected delay at ultrafast speed

Aug 05, 2011

Molecules that suddenly transform into new structures when stimulated by photons or electrons play key roles in many chemical and biological processes. Recently, chemists have discovered that adding transition ...

Diode lights offer bright future for low energy

May 13, 2009

German scientists said Wednesday they had tweaked organic light-emitting diodes (OLEDs) -- the materials used in flat-screen TVs, laptop computer screens and mobile phone displays -- to become flexible, energy-efficient ...

Berkeley Researchers Light Up White OLEDs

Apr 06, 2010

(PhysOrg.com) -- Light-emitting diodes, which employ semiconductors to produce artificial light, could reduce electricity consumption and lighten the impact of greenhouse gas emissions. However, moving this ...

Recommended for you

Team pioneers strategy for creating new materials

3 hours ago

Making something new is never easy. Scientists constantly theorize about new materials, but when the material is manufactured it doesn't always work as expected. To create a new strategy for designing materials, ...

Plug n' Play protein crystals

8 hours ago

Almost a hundred years ago in 1929 Linus Pauling presented the famous Pauling's Rules to describe the principles governing the structure of complex ionic crystals. These rules essentially describe how the ...

Breaking benzene

Aug 27, 2014

Aromatic compounds are found widely in natural resources such as petroleum and biomass, and breaking the carbon-carbon bonds in these compounds plays an important role in the production of fuels and valuable ...

User comments : 0