Michael A. Greenwood
Although the efficiency of organic LEDs (OLEDs) has improved steadily in recent years, it remains challenging to manufacture the intricate, multilayered devices.
Researchers at the Institut für Hochfrequenztechnik at the Technische Universität Braunschweig, Germany, who are seeking to overcome the complex process, have created highly efficient OLEDs with only two organic layers. The result is an OLED that performs well but uses less organic material than other approaches and thus is significantly easier to fabricate.
The device created by the research team had just one hole transport layer, one electron transport layer and a phosphorescent emitter material. The key to the simplified process was a tungsten oxide anode, through which a direct hole injection into wide gap materials was possible. More complex fabrication techniques require multiple hole transport layers. Fewer materials result in a process that is quicker and less expensive.
During experiments with the simplified OLED, efficiency exceeded 40 lm/W and 45 cd/A at a brightness of 100 cd/m2, results that are unsurpassed by other comparably simple OLEDs, the researchers said.
The results suggest that the technique could be used for fail-safe manufacturing processes.
Applied Physics Letters, Sept. 10, 2007, Vol. 91, 113506.
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