Chlorine layer reduces OLED device complexity

By engineering a one-atom-thick sheet of chlorine onto the surface of an existing industry-standard electrode material (indium tin oxide [ITO]) found in today’s flat-panel displays, the researchers from the Department of Materials Science and Engineering at the University of Toronto have created a medium that allows for efficient electrical transport while eliminating the need for several costly layers found in traditional OLED devices.

‘It turns out that it’s remarkably easy to engineer this one-atom-thick layer of chlorine onto the surface of ITO,’ said Michael G Helander. ‘We developed a UV light-assisted process to achieve chlorination, which negates the need for chlorine gas, making the entire procedure safe and reliable.’

The team — including Zhibin Wang and project lead Prof Zheng-Hong Lu — tested their green-emitting ‘Cl-OLED’ against a conventional OLED and found that the efficiency was more than doubled at very high brightness.

‘OLEDs are known for their high efficiency,’ said Helander. ‘However, the challenge in conventional OLEDs is that as you increase the brightness, the efficiency drops off rapidly.’

Using the chlorinated ITO, the advanced materials researchers found that they were able to prevent this drop-off and achieve a record efficiency of 50 per cent at 10,000cd/m² (a standard fluorescent light has a brightness of approximately 8,000cd/m²), which is at least two times more efficient than the conventional OLED.

‘Our Cl-ITO eliminates the need for several stacked layers found in traditional OLEDs, reducing the number of manufacturing steps and equipment, which ultimately cuts down on the costs associated with setting up a production line,’ said Zheng-Hong Lu.

‘This effectively lowers barriers for mass production and thereby accelerates the adoption of OLED devices into mainstream flat-panel displays and other lighting technologies.’