Metal-halide-based perovskites perform excellently in semiconducting applications. Their structure can be constructed into a polycrystalline thin film via a solution approach without high-temperature treatment that has high capacity in applying to large areas and flexible substrates. These materials have strong photoluminescence features, a tunable bandgap, and a narrow full width at half maximum of the luminescence spectra. These features make them attractive for application in light-emitting diodes.
Organometal halide perovskite light emitting diodes exhibit a current efficiency of more than 42.9 cdA-1 on green light emission by reducing the grain sizes of the perovskite film implementing the nanocrystal pinning method. This shows high possibility for integration into lighting devices. In the recent days, an all-inorganic perovskite nanocrystals CsPbX3 prepared by the solution-phase chemistry method have been reported by a number of researchers. These nanocrystals have indicated excellent thermal stability as well as high photoluminescence quantum yield extending up to 905 in solution.
The superior features of the CsPbX3 nanocrystals make them promising for electroluminescence applications. In fact, several researchers have continued to investigate LEDs that implement CsPbX3 nanocrystals. However, researchers are still investigating blue perovskite light-emitting diodes, which will be necessary for display applications.
Researchers led by Professor Yang Yang at the University of California demonstrated a high brightness of the blue all-inorganic perovskite light emitting diodes with narrow full width at half maximum of the electro luminescence and photoluminescence spectra by tuning the dispersity of the CsPbX nanocrystals in the deposition solution in a bid to establish perovskite films grain size. Their research work is published in Advanced Materials.
The authors derived blue-emission Cs-based perovskite nanocrystals by mixing directly synthesized bromide and chloride nanocrystals in a weight ratio of 2:1. They obtained high-brightness blue perovskite light-emitting diodes by tuning the size of the perovskite film grains. The researchers also demonstrated a white perovskite light emitting diode for the first time by mixing orange polymers with blue perovskite nanocrystals as the active layer. They analyzed, through time resolved photoluminescence, exciton transfer from blue nanocrystals to the orange polymers through Dexter energy transfer or Forster. Pure white light was realized when the ratio between the perovskite nanocrystals and the polymers.
The research team synthesized CsPbBrxCl3-x nanocrystals in order to realize blue shift emission with a peak at 470nm and a narrow bandwidth. They controlled the sizes of the nanocrystals in the light emission layer at about 15nm, which led to a better quantum-confinement effect.
The authors designed the preferred structure and realized a brightness of about 350 cdm-2. In view of the high brightness blue perovskite light emitting diodes, the white light emitting diode could be derived by integrating poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] directly into the active layer with the Commission Internationale de l’Eclairage chromaticity coordinate at (0.33,0.34).
The researchers also found that they could tune the purity of the white light emitting diode by changing the ratio between the two different emissive materials and also by tuning the ratio between the halogen on the perovskite crystals. This demonstrated a high potential in applications such as lighting gadgets and displays in the future.
En-Ping Yao, Zhanlue Yang, Lei Meng, Pengyu Sun, Shiqi Dong, Ye Yang, and Yang Yang. High-Brightness Blue and White LEDs based on Inorganic Perovskite Nanocrystals and their Composites. Advanced Materials 2017, 29, 1606859.
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