Pure-Organic OLEDs Could Enable Device Mass Production
POHANG, South Korea — Highly efficient, solution-processed fluorescence organic LEDs (OLEDs) have been fabricated using "pure-organic" emitters and could enable mass-production of the devices.
Conventional OLEDs use phosphorescent emitters which have shown high internal quantum efficiency (IQE) of nearly 100 percent. However, those emitters incorporate expensive, precious heavy metals such as iridium and platinum into phosphorescent metal complexes, which has limited their commercialization.
In order to overcome these disadvantages, the research team from Pohang University of Science & Technology (Postech) has used pure-organic thermally activated delayed fluorescence (TADF) emitters which the team said show a very high IQE of nearly 100 percent without incorporating precious metals. TADF emitters also offer the advantages of easy synthesis using pure-organic molecules and versatile molecular design, reducing the cost of synthesis.
The Postech team, led by professor Tae-Woo Lee, introduced the inexpensive, simple solution-process to fabricate the TADF-OLEDs by solving fundamental problems which had limited the high efficiency in solution-processed TADF-OLEDs. They created a multifunctional buffer hole injection layer (HIL) that increased the hole injection capability to the emitting layer (EML) due to its high work function.
The researchers also improved the luminescence efficiency of TADF-OLEDs by preventing exciton quenching at the HIL/EML interface. They also reported that a 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 could remedy the disadvantages of a complex and expensive vacuum-deposition process and thus lower the production cost of the devices.
"This technology is a big leap toward the development of inexpensive and solution-processed OLED displays and solid-state lightings because this method uses only low-cost, pure-organic molecules and simple solution process to realize the extremely high efficiency solution-processed OLEDs,” said Lee.
The research was published in Advanced Materials (doi: 10.1002/adma.201504490).
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