Imma Perfetto
Cosmos science journalist
Electric lighting revolutionised human society in the late 19th century, but we’ve come a long way from the incandescent bulbs of old.
Major lighting systems today, from the screen on which you’re reading this to your car’s headlights, rely on light-emitting diodes (LEDs). These use semiconductors to turn electricity into light in a much more efficient and durable way.
Blue LEDs are used to create white light and are essential for general lighting applications. Scientists have now developed a new way to produce a safe, stable and ultra-bright material for generating high-performance blue LEDs.
“Deep blue LEDs are at the heart of today’s energy-efficient lighting technologies,” says Jing Li, a professor of chemistry and chemical biology who led the study at Rutgers University, USA.
“However, existing options often present issues with stability, scalability, cost, efficiency or environmental concerns due to the use of toxic components.
“We wanted to create new kind of materials that give very bright deep blue light and use them to fabricate LEDs at lower cost than current blue LEDs.
“This new copper-iodide hybrid offers a compelling solution, leveraging its non-toxicity, robustness and high performance.”
The team developed a new manufacturing technique called “dual interfacial hydrogen-bond passivation” to produce the material. The process is described in a paper in the journal Nature.
Within an LED semiconductor material, electrons recombine with “electron holes” (where there is no electron) to release energy in the form of photons.
“Our processing method minimises defects that can impede the movement of electric charges at the interface of these hybrid materials,” says first author Kun Zhu, a former graduate student and postdoctoral researcher at Rutgers. “This approach could be a versatile strategy for generating high-performance LEDs.”
The researchers found their new material has a “photoluminescence quantum yield” of about 99.6%. This means it converts nearly all the photoenergy it receives into blue light.
Blue LEDs manufactured with this material reached a “maximum external quantum efficiency” – the ratio between the number of emitted photons and number of injected electrons – of 12.6%, which is among the highest achieved so far for solution-processed deep blue LEDs.
The researchers also note that the deep blue LEDs have “excellent operational stability” under normal conditions. They can be turned on for 204 hours before becoming half as bright.
“Overall, this type of new material is paving the way for better, brighter and longer-lasting LEDs,” Li says.