Perovskite boost for LEDs

November 08, 2018 // By Nick Flaherty
Researchers in Cambridge have set a new efficiency record for LEDs based on perovskite materials, rivalling the organic OLED versions.

The perovskite devices developed at the University of Cambridge can be made at much lower costs, and can be tuned to emit light across the visible and near-infrared spectra with high colour purity. The work is led by plastic display pioneer Prof Sir Richard Friend as perovskite LED films can be made thin and flexible. 

The researchers have engineered the perovskite layer in the LEDs to show close to 100% internal luminescence efficiency, opening up future applications in display, lighting and communications. "The best external quantum efficiencies of these devices are higher than 20% at current densities relevant to display applications, setting a new record for perovskite LEDs, which is a similar efficiency value to the best OLEDs on the market today," said Baodan Zhao, first author of the paper in the journal Nature Photonics.

While perovskite-based LEDs have already been developed, they have not been nearly as efficient as conventional OLEDs at converting electricity into light. Earlier hybrid perovskite LEDs, first developed by Prof Friend's group at the Cavendish Laboratory four years ago, were promising, but the losses from the perovskite layer, caused by tiny defects in the crystal structure, limited the light-emission efficiency.

Now the same group has shown that by forming a composite layer of the perovskites together with a polymer, it is possible to achieve much higher light-emission efficiencies, close to the theoretical efficiency limit of thin-film OLEDs.

"This perovskite-polymer structure effectively eliminates non-emissive losses, the first time this has been achieved in a perovskite-based device," said Dr Dawei Di from Cambridge's Cavendish Laboratory, one of the authors of the paper. "By blending the two, we can basically prevent the electrons and positive charges from recombining via the defects in the perovskite structure."

The perovskite-polymer blend used in the LED devices, known as a bulk heterostructure, is made of two-dimensional and three-dimensional perovskite components and an insulating polymer. When an ultra-fast laser is shone on the structures, pairs of electric charges that

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