Manganese may pave the way for inclusion of organic light-emitting diodes in consumer electronics

Manganese nodule. (Reference image by Hannes Grobe, Wikimedia Commons.)

White and green organic light-emitting diodes (OLEDs) displaying record high efficiency have been developed by researchers at Korea’s Dongguk University.

To be able to create the OLEDs, the scientists first manufactured a new environmentally friendly and cost-effective bright green light-emitting manganese complex called MnBz.

Until now, one of the most popular commercial methods for fabricating OLEDs was the solution processing approach. However, while the fabrication process of such LED itself is low-cost and simple, the raw materials used during the solution process often include precious and expensive metals driving up the fabrication costs.
Studies have shown that low-dimensional complexes of earth-abundant transition metals could be the key to solving this problem. Thus, to develop a promising solution using this approach, the Dongguk team led by Vijaya Gopalan Sree attempted to synthesize zero-dimensional manganese (Mn)-based complexes via solution processing.

“Replacing expensive metals like gold and platinum with crystalline earth-abundant transition metal complexes can help achieve lightning solutions or displays that are cheaper yet bright and vibrant,” Sree said.
In this study, which was published in the Chemical Engineering Journal, Sree and his colleagues synthesized MnBz by subjecting manganese bromide (MnBr2) and benzyl-triphenylphosphonium bromide (Ph3BzPBr) to solvent-free grinding, followed by dissolution in acetonitrile solvent. The resulting solution was slowly evaporated over days to obtain single crystals of MnBz. The obtained MnBz exhibited bright green-light emissions with a narrow emission spectrum and high quantum yield.
The team then used the single crystals of MnBz to design a novel Mn(II) complex-based warm-white light-emitting device, which exhibited an excellent colour rendering index (CRI) of 78. MnBz was also used to design a green phosphorescent OLED device, which exhibited excellent performance. These light emitters displayed a record-breaking quantum efficiency of 11.42% and a current efficiency of 56.84 cd A-1.
The exceptional brightness of these MnBz-based devices in response to low turn-on voltages can pave the way for energy-efficient OLED-based consumer electronics and lighting systems.

“Our new eco-friendly and cost-effective light emitter can facilitate developments towards a wider adoption of OLEDs and ultimately impact people’s lives by transforming the way we interact with and illuminate our world,” Sree said.