Low-cost perovskite LEDs now super efficient

November 19, 2018 | 07:12
Low-cost perovskite LEDs now super efficient
Low-cost perovskite LEDs now super efficient
Researchers working at the University of Cambridge have achieved a new efficiency record for perovskite-based LEDs comparable to the best organic LEDs (OLEDs).

OLED display technology is expensive and is consequently only used on high-end TVs and smart devices. The new perovskite-based LEDs can be made much cheaper and are able to be tuned to emit high colour-purity light in the visible and near IR range. The perovskite layer in the LED has been engineered to achieve near 100% internal luminescence, making it an attractive low-cost display technology for next-generation displays, lighting and even solar cells.

Perovskite material has already been used to build highly-efficient solar cells which could one day replace commercial silicon solar cells. Up till now, research into perovskite LEDs has not been so successful in producing devices anywhere near as efficient as OLEDs. Hybrid perovskite LEDs showed promise but minute defects in the crystalline structure of the perovskite layer limited the radiation output.

Now, Cambridge researchers have shown that forming a composite layer of perovskite and a polymer makes it possible to achieve significantly higher light emissions, which are close to the theoretical maximum efficiency of thin-film OLEDs. Their results are published under the title ‘High-efficiency perovskite-polymer bulk heterostructure light-emitting diodes’ in the journal Nature Photonics.

The new perovskite-polymer composite structure is said to significantly reduce non-emissive losses. The composite blend prevents the electrons and positive charges from recombining via defects in the perovskite structure.

The perovskite polymer mixture (mass heterostructure) used in this new LEDs consists of two- and three-dimensional perovskite components together with an insulating polymer. When an ultrafast laser strikes the structures, pairs of electrical charges that transfer energy move from the 2D areas to the 3D areas in a trillionth of a second. The charges dispersed in the 3D areas then recombine and emit light extremely efficiently. The speed at which this process occurs means that the charges in the 3D areas are effectively isolated from the defects by the polymer to prevent energy losses. 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.

The team is working to improve the long-term stability of the product. When the first examples were built, the perovskite LEDs lasted only a few seconds, but now after four years research and development they achieve a half-life of almost 50 hours.

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