Conventional OLEDs use the phosphorescent emitters which have shown high internal quantum efficiency (IQE) of nearly 100%. However, they should incorporate precious heavy metals such as iridium and platinum into phosphorescent metal-complexes; these limit their commercialization.
In order to overcome the drawbacks, the research team, which was led by Prof. Tae-Woo Lee (Dept. of Materials Science and Engineering) at POSTECH, uses pure-organic TADF emitters which can show a high IQE of about 100% without precious metals. TADF emitters benefit from easy synthesis using pure-organic molecules and versatile molecular design which helps reduce synthesis costs.
TADF emitters have also introduced the inexpensive, simple solution-process to fabricate the TADF-OLEDs by solving fundamental problems which limit the high efficiency in solution processed TADF-OLEDs. A multi-functional buffer hole injection layer (Buf-HIL) that can increase the hole injection capability to the emitting layer (EML) due to its high work function, and also improve the luminescence efficiency of TADF-OLEDs by preventing exciton quenching at the HIL/EML interface was employed. Furthermore, new polar aprotic solvent improved the device efficiency by improving the solubility of pure-organic TADF emitters, reducing the surface roughness and the aggregation of dopants, and managing the exciton quenching in the emitting layer.
The improvement in solution processed TADF-OLEDs helps to counter the disadvantages of a complex and expensive vacuum-deposition process which leads to lower the production cost of the devices.