Organic light-emitting diodes (OLEDs) have revolutionised modern electronics. Instead of the old, incandescent lamps that made light by heating a wire filament until it glowed (much like how a normal lamp works), OLEDs give off light when electrons zap through diodes. This is more energy efficient and uses up far less space. One issue not yet resolved however – and strongly requested by the electronics industry – is highly efficient blue pixels.
Achieving electronic efficiencies
The HyperOLED project was launched to develop a highly efficient blue OLED material with enhanced lifetime. It also sought to find new ways of simplifying the manufacture of OLEDs. The ultimate objective was to enable manufacturers to produce consumer electronics goods and displays more efficiently. “To achieve this, we began by collecting and analysing material data from thousands of electronic devices,” explains HyperOLED coordinator Christof Pflumm, lead expert in performance materials at Merck, Germany. A key result of the project has been the successful development of a highly efficient blue OLED material system, integrated into a white OLED stack, with a reduced number of layers and a low driving voltage. “The techniques pioneered in HyperOLED demonstrated that the number of layers in OLED stacks could be reduced,” says Pflumm. “This could save on material and open up the possibility of more efficient manufacturing of high-resolution electronic devices.” In the course of these investigations, the project also revealed the importance of energy transfer processes and the limitations of common measurement techniques in their characterisation. This demonstrated to the team how further energy efficiency improvements in OLEDs could be achieved. Models were developed to support tests on how well energy losses in electronic devices could be suppressed. These showed how the molecular design of fluorescent emitters could be altered to suppress losses.
Speeding up development
Taken together, Pflumm believes that the project’s results will have a profound impact on the way hyperfluorescent devices are made in the future. The project’s search for new OLED materials and methods to measure performance has already resulted in nine patent applications. “This project has provided numerous novel insights and methods in the field of hyperfluorescent OLEDs,” he says. “Our findings will contribute to a better understanding of the underlying physical mechanisms and will thus help to speed up development.” Due to the novelty of the materials developed, integrating HyperOLED’s innovations directly onto a micro display production line was not feasible. “Due to technical issues which we could identify, we couldn’t obtain sufficient performance in terms of colour point and device stability for direct application in consumer products,” says Pflumm. Nonetheless, a workflow involving coating, final processing and characterisation was successfully developed. The project has also provided developers and manufacturers with valuable guidance in terms of strategic decisions on further material development. The results will also serve as the basis for further collaboration between the project’s industrial partners. “A key aim was making this knowledge available to the whole scientific community,” says Pflumm. “This is reflected in the number of publications we have produced, and the submission of articles is still ongoing even after project completion.”
HyperOLED, OLED, organic light-emitting diodes, hyperfluorescent, electronic, diodes, electron