Cheap electronic devices can be printed using commercial printing presses thanks to light-emitting colloidal inks developed by US scientists.

Stephen Foulger and colleagues from Clemson University made colloidal particles from organic molecules that emit red, blue or green light. They used different ratios of the particles to make organic light emitting devices (OLEDs) in a wide range of colours.

A variety of colours can be obtained using different ratios of the light-emitting particles in the colloidal inks

The light emitting molecules are in a water-based colloid so they can be used as ink in commercial high-volume printing techniques, explains Foulger. The team printed the colloidal particles onto a conductive surface and lit up the printed pattern by applying a voltage across the surface. Foulger says the particles could be used to make coloured electronic displays for car dashboards, for example, and adds that this combination of low cost starting materials and high volume printing will mean cheaper products.

'The most significant finding is that individual colour has been realised in a colloidal particle and each colloidal particle still emits its original colour even when mixed together in the OLED,' says Hideyuki Murata, an expert in organic electroluminescence at the Advanced Institute of Science and Technology, Ishikawa, Japan.

Foulger says the results will help bring printable electronics to the market quickly. 'We are continuing to improve the luminosity of the devices and reduce defects in printed structures,' he adds. 'The next step is improving yields and transitioning the technology to full-scale printing presses.'

Rachel Cooper