High-Brightness Blue and White LEDs based on Inorganic Perovskite Nanocrystals and their Composites

Significance 

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.

High-Brightness Blue and White LEDs based on Inorganic Perovskite Nanocrystals and their Composites. Advances in Engineering

About the author

En-Ping Yao received his B.S. and Ph.D. degrees in Electrical Engineering from National Cheng Kung University, Tainan, Taiwan, in 2009 and 2015, respectively. He was a postdoctoral researcher with expertise on organic photovoltaics, perovskite photovoltaics, and perovskite light-emitting diodes in Yang Yang’s Lab., Department of Materials Science and Engineering, University of California, Los Angeles (UCLA) from 2015 to 2017. He is doing postdoctoral research on optoelectronic dynamics of perovskites in Chair for Photonics and Optoelectronics, Ludwig-Maximilians-Universität München (LMU).

About the author

Zhanlue Yang received his B.S. degree in Department of Chemistry from Tsinghua University, China in 2015. His research mainly focused on exploring perovskite light-emitting materials with novel structure and components. He received his M.S. degree in Yang Yang’s Lab, Department of Materials Science and Engineering, University of California.

About the author

Lei Meng received his B.S. from Shanghai Jiao Tong University, M.S. from Northwestern University in 2012 and Ph.D. in Materials Science and Engineering from University of California, Los Angeles (UCLA) in 2017, respectively. Lei Meng is currently working as research associate in UCLA and mainly focusing on photovoltaic semiconductor materials. He has expertise in the fields of organic photovoltaics and high performance perovskite optoelectronic devices.

About the author

Pengyu Sun graduated with a B.S. in optical science and engineering from Fudan University in 2013. He is currently a Ph.D. candidate in materials science and engineering under the guidance of Professor Yang Yang. His research interests include optoelectronics of perovskite materials and solar cells and metal oxide semiconductors.

About the author

Shiqi Dong received her B.S degree in Microelectronics from Fudan University, Shanghai, China in 2014. She is currently a graduate student in Department of Materials Science and Engineering, University of California, Los Angeles.

About the author

Yang Yang received his M.S. and Ph.D. in Physics and Applied Physics from the University of Massachusetts, Lowell in 1988 and 1992, respectively. Before he joined UCLA in 1997, he served as the research staff in UNIAX (now DuPont Display) from 1992 to 1996. Yang is now the Carol and Lawrence E. Tannas Jr Endowed Chair Professor of Materials Science at UCLA. He is also the Fellow of SPIE, RSC and the Electromagnetic (EM) Academy. He is an expertise in the fields of organic, inorganic and organic/inorganic hybrid electronics and the development and fabrication of related devices, such as photovoltaic cells, LEDs, transistor and memory devices.

Reference

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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