07-Nov-2018 - University of Cambridge

New efficiency record set for perovskite LEDs

Researchers have set a new efficiency record for LEDs based on perovskite semiconductors, rivalling that of the best organic LEDs (OLEDs).

Compared to OLEDs, which are widely used in high-end consumer electronics, the perovskite-based LEDs, developed by researchers 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 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, as well as next-generation solar cells.

These perovskite materials are of the same type as those found to make highly efficient solar cells that could one day replace commercial silicon solar cells. 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 Professor Sir Richard Friend's group at the University's Cavendish Laboratory four years ago, were promising, but losses from the perovskite layer, caused by tiny defects in the crystal structure, limited their light-emission efficiency.

Now, Cambridge researchers from the same group and their collaborators have 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 corresponding 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 carry energy move from the 2D regions to the 3D regions in a trillionth of a second: much faster than earlier layered perovskite structures used in LEDs. Separated charges in the 3D regions then recombine and emit light extremely efficiently.

"Since the energy migration from 2D regions to 3D regions happens so quickly, and the charges in the 3D regions are isolated from the defects by the polymer, these mechanisms prevent the defects from getting involved, thereby preventing energy loss," said Di.

"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, the paper's first author.

While perovskite-based LEDs are beginning to rival OLEDs in terms of efficiency, they still need better stability if they are to be adopted in consumer electronics. When perovskite-based LEDs were first developed, they had a lifetime of just a few seconds. The LEDs developed in the current research have a half-life close to 50 hours, which is a huge improvement in just four years, but still nowhere near the lifetimes required for commercial applications, which will require an extensive industrial development programme. "Understand the degradation mechanisms of the LEDs is a key to future improvements," said Di.

Facts, background information, dossiers
  • LEDs
  • perovskite LEDs
  • electrons
  • isolating polymers
  • perovskite-polymer…
More about University of Cambridge
  • News

    Smog-eating graphene composite reduces atmospheric pollution

    Graphene Flagship partners the University of Bologna, Politecnico di Milano, CNR, NEST, Italcementi HeidelbergCement Group, the Israel Institute of Technology, Eindhoven University of Technology, and the University of Cambridge have developed a graphene-titania photocatalyst that degrades u ... more

    'Messy' production of perovskite material increases solar cell efficiency

    Scientists at the University of Cambridge studying perovskite materials for next generation solar cells and flexible LEDs have discovered that they can be more efficient when their chemical compositions are less ordered, vastly simplifying production processes and lowering cost. The surpris ... more

    'Artificial leaf' successfully produces clean gas

    A widely-used gas that is currently produced from fossil fuels can instead be made by an 'artificial leaf' that uses only sunlight, carbon dioxide and water, and which could eventually be used to develop a sustainable liquid fuel alternative to petrol. The carbon-neutral device sets a new b ... more

  • Videos

    Graphene: A 2D materials revolution

    Graphene is a two-dimensional material made up of sheets of carbon atoms. With its combination of exceptional electrical, mechanical and thermal properties, graphene has the potential to revolutionise industries ranging from healthcare to electronics. more

    Where there’s muck there’s aluminium (if not brass)

    Technology developed in Cambridge at the Department of Chemical Engineering and Biotechnology lies at the heart of a commercial process that can turn toothpaste tubes and drinks pouches into both aluminium and fuel in just three minutes. The process recycles a form of packaging – plastic-al ... more

    Nanomaterials Up Close: Gum Arabic

    This alien glob is a piece of gum arabic from the hardened sap of the Acacia tree, most likely collected from a tree in Sudan. Rox Middleton, from the University of Cambridge, explains how the electron microscope has changed the way we are able to interact with objects at the nanoscale, all ... more