Greater illumination on inorganic perovskite LEDs

29 March 2019

Material scientists have developed a more efficient way to produce brighter, all-inorganic perovskite LEDs with a half-lifetime of over 250 hours.

A Hong Kong-based researcher and his team have developed an efficient fabrication method to make all-inorganic perovskite films with improved optical properties and stability compared with existing technologies.

Professor Andrey Rogach (Croucher Senior Research Fellowship 2019), of the Department of Materials Science and Engineering, City University of Hong Kong, and his research group, working in collaboration with Shanghai University scientists, have devised a way to rapidly generate small-grained perovskite crystals, producing smooth and pinhole-free perovskite films.

Metal halide perovskites – structured compounds of metals with chlorine, bromine or iodine – have been regarded as promising materials for solution-processed light emitting diodes (LEDs) owing to their excellent optical properties, such as saturated emission colours and easy colour tunability. However, inorganic perovskite LEDs tend to exhibit relatively poor electro-luminescence performance due to their large perovskite grain sizes.

In the recent findings, published in Nature Communications, the researchers generated CsPbBr3 perovskite crystals based on inorganic caesium (Cs), lead (Pb) and bromine (Br). They discovered that using caesium trifluoroacetate (TFA) as the caesium source resulted in interactions that greatly improved the crystallisation rate of perovskite films while suppressing surface defects.

Using their technique, the researchers fabricated stable green perovskite LEDs with a maximum current efficiency of 32.0 cd/A, corresponding to an external quantum efficiency of 10.5 per cent, regarded as satisfactory in current perovskite LEDs.

More importantly, their all-inorganic perovskite LEDs had a half-lifetime of over 250 hours at an initial luminance of 100 cd/m2, an operational lifetime 17 times greater than CsBr-derived perovskite LEDs.

“Our study suggests that high colour purity and low-cost all-inorganic lead halide perovskite films can be developed into highly efficient and stable LEDs via a simple optimisation of grain boundaries,” Rogach said.

He also foresaw significant application potential for such films. “They are easy to fabricate and can be easily deposited by printing to realise various optoelectronic devices.”

Professor Andrey L. Rogach is Chair Professor of Photonics Materials in the Department of Materials Science and Engineering, and Founding Director of the Centre for Functional Photonics at City University of Hong Kong. In 2018, he was the only Hong Kong recipient of the Carl Friedrich von Siemens Research Award, presented by the Alexander von Humboldt Foundation. His research focuses on the synthesis, assembly and optical spectroscopy of semiconductor and metal nanocrystals and their hybrid structures, as well as their use for energy-related and optoelectronic applications, including photocatalytic hydrogen generation from water, photodetectors, light emitting devices, and displays. He received a Croucher Senior Research Fellowship in 2019.

To view Professor Rogach’s Croucher profile, please click here.