This is how perovskites are produced for efficient LEDs

Researchers at LiU, together with colleagues in China, have shown how it is possible to obtain efficient LEDs in perovskite. In an article in Nature Communications, they provide guidelines on how high-quality light-emitting perovskites should be manufactured.

Sai Bai and Zhongcheng Yuan, Biomolecular and Organic Electronics;  Biomolecular and Organic ElectronicsSai Bai and Zhongcheng Yuan, together with colleagues, have found the recipe for high-efficiency LEDs in perovskite.Charlotte Perhammar

 

Perovskites are a family of materials defined by their crystal structure. Halida perovskites are easy to manufacture in a solution consisting of both metallic and organic halides. It provides perovskites with excellent optical and electrical properties suitable for various optoelectric applications, such as solar cells, LEDs and photodetectors.

Sai Bai and Zhongcheng Yuan, Biomolecular and Organic Electronics;  Biomolecular and Organic ElectronicsManufacture of LEDs in perovskite.
Charlotte Perhammar
However, during manufacture, defects in the material occur, defects that make thetransport of cargo more difficult. When these defects are taken care of, passivated, it affects the crystallization process which therefore needs to be carefully controlled. The research team at LiU, under the leadership of the university lecturer Feng Gao, together with researchers at Nanjing Tech University and Soochow University in China, studied how the various components of the solution affect the crystallization process and what happens at the interfaces.

The defects are passivated

– We and several other groups have realized that by adding an extra amount of organic halides in the solution, we can help passivate the defects to produce high-emitting films in perovskite, says Zhongcheng Yuan, PhD student at the Department of Physics, Chemistry and Biology, IFM , at Linköping University.

But an excess of organic halides also causes the crystallization process, which gives the special and necessary perovskite structure, to be complicated.

The researchers have now solved this dilemma by adding a metal oxide, in this case zinc oxide, to support the crystallization process. The zinc oxide helps to remove enough of the extra organic cations (positively charged ions) to speed up the process. The article in Nature Communications shows how chemical reactions between different metal oxide layers and the perovskite layer affect the properties of the thin films of perovskite, and thus also the performance of the LED.

– We can now control the process effectively by utilizing the zinc oxide’s ability to remove the unwanted organic cations while still retaining the desired halide anions, says Sai Bai, a researcher at IFM who, together with Feng Gao, is the main author of the article.

Most effective in the world

Sai Bai and Zhongcheng Yuan, Biomolecular and Organic Electronics;  Biomolecular and Organic ElectronicsThe film containing zinc oxide, the darkest, provides the best light emitting properties.Charlotte PerhammarThis new discovery, in combination with previous results where the group found solutions to deal with the defects in the material, has made it possible to make efficient light-emitting perovskite films in the laboratory. The LEDs that result are light near the infrared with an efficiency of 19.6 percent, that is, 19.6 percent of the electrons sent into the material give rise to light, photons. It is one of the best results in the world for perovskite LEDs.

– Perovskites are a promising field of research. We have seen a number of breakthroughs over the past five years, but the field is still new and much work remains before the perovskite LEDs can be produced commercially and on a large scale. A critical aspect we need to improve is the stability of the LEDs, says Feng Gao.

Footnote:  Halides are, for example, fluorides, chlorides bromines, common substances with one thing in common – they contain a halogen (fluorine chlorine, bromine, etc.)

The research was funded by Feng Gao’s ERC Starting Grant, the European Commission’s Marie Skłodowska-Curie Actions and the National Key Research and Development Program of China, among others

Unveiling the synergistic effect of precursor stoichiometry and interfacial reactions for perovskite light-emitting diodes , Zhongcheng Yuan, Yanfeng Miao, Zhangjun Hu, Weidong Xu, Chaoyang Kuang, Kang Pan, Pinlei Liu, Jingya Lai, Baoquan Sun, Jianpu Wang, Sai Feng Gao, Nature Communications 2019, DOI 10.1038 / s41467-019-10612-3

Sai Bai and Zhongcheng Yuan, Biomolecular and Organic Electronics;  Biomolecular and Organic ElectronicsSai Bai and Zhongcheng Yuan in the laboratory. Charlotte Perhammar