AsianScientist (Feb. 26, 2019) – Researchers in China have developed an efficient fabrication method to produce all-inorganic perovskite films with better optical properties and stability than existing technologies. Their findings are published in the journal Nature Communications.
Perovskites of metal halide—structured compounds of metals with chlorine, bromine or iodine—have recently attracted a lot of attention as promising materials for solution-processed light emitting diodes (LEDs) owing to their excellent optical properties, such as saturated emission colors and easy color tunability.
In particular, perovskites based on inorganic cesium (Cs) and lead (Pb) cations, namely CsPbX3, where X can be chlorine (Cl), bromine (Br) and iodine (I), exhibit better thermal and chemical stability compared to the organic-inorganic ‘hybrid’ metal halide perovskites. However, inorganic perovskite LEDs tend to exhibit relatively poor electro-luminescence performance due to their large perovskite grain sizes.
In his study, a team of researchers at the City University of Hong Kong (CityU) and Shanghai University, China, has found a way to rapidly generate small-grained CsPbBr3 perovskite crystals by using cesium trifluoroacetate (TFA) as the cesium source, producing smooth and pinhole-free perovskite films. They found that the TFA anions interacted with Pb2+ cations in the CsPbX3 precursor solution to greatly improve the crystallization rate of perovskite films while suppressing surface defects.
Using their technique, the researchers fabricated stable green perovskite LEDs with a maximum current efficient of 32.0 cd/A corresponding to an external quantum efficiency of 10.5 percent—a level generally considered as satisfactory in existing 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, which is a 17-times improvement in operational lifetime compared with CsBr-derived perovskite LEDs.
“Our study suggests that the high color-purity and low-cost all-inorganic lead halide perovskite films can be developed into highly efficient and stable LEDs via a simple optimization of the grain boundaries,” said Professor Andrey Rogach at CityU, a corresponding author of the paper.
“I foresee significant application potential of such films, as they are easy to fabricate and can be easily deposited by printing to realize various optoelectronic devices,” he added.
Source: City University of Hong Kong; Photo: Shutterstock.
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