Perovskite light emitters 

 Metal halide perovskites have become a promising class of light-emissive materials for next-generation displays due to numerous excellent optical/electrical properties such as high photoluminescence quantum efficiency, very narrow emission linewidth, high charge carrier mobility, low energetic disorder, solution processability, simple color tuning, and low material cost.

 However, the following challenges must be overcome to realize the successful commercialization of perovskite emitters.

 1) Toxicity of lead (Pb)

 2) Low material/device stability

 3) Low device efficiency of blue perovskite LEDs

 4) Photo-induced halide segregation

 Our group aims to overcome these challenges by combining Surface Chemistry and Device Engineering.

 We envision our research on perovskite emitters will lead to a new mainstream in the display industry: "Perovskite Displays" or "PeLED Displays".

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Research highlight:

[1] H. Cho et al., Science 2015, 350(6265), 1222-1225

[2] H. Cho et al., Advanced Materials 2018, 30(42), 1704587

[3] Y. Kim and H. Cho et al., Proceedings of the National Academy of Sciences of the United States of America (PNAS) 2016, 113(42), 11694–11702

Surface/interface engineering of colloidal quantum dots

 Colloidal quantum dots (QDs) based on II-VI (e.g., CdSe, ZnSe) or III-V (e.g., InP) compound semiconductors are useful low-dimensional building blocks for light-emitting diodes and displays because of their high PLQY approaching unity, high color purity (i.e., narrow emission spectra), and continuously-tunable emission colors controlled by the QD size, composition, and structure. Furthermore, the durability of QDs combined with their solution processability enabled rapid growths of commercial QD displays as well as their use in optoelectronics and sensors.

  Despite the numerous advantages, CdSe-based QDs cannot be used in industry because the RoHS directive restricts the use of toxic cadmium in electronics. Therefore, it is essential to develop environmentally benign QDs while maintaining the excellent optical properties of CdSe QDs.

 Colloidal QDs typically have a core/shell structure and surface ligands to increase the luminescence efficiency and maintain the material/colloidal stability. Our group focuses on the development of environmentally benign core/shell QDs where the composition, size, shape, shell structure, and surface ligands of QDs are tailored for LED applications.

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Research highlight:

[1] H. Cho et al., Advanced Materials 2020, 32(46), 2003805 

Perovskite & QD LEDs

 Device engineering of perovskite LEDs and QD LEDs is crucial for achieving high-efficiency and high-stability devices. Particularly, improving the low stability of perovskite LEDs and QD LEDs (particularly,  blue LEDs) is an essential task that must be completed to realize self-emissive displays based on perovskites and quantum dots.

 Our group pursues a deep understanding of structure-property relationships to solve the problems. In other words, we are interested in analyzing how material parameters (such composition, shell, dimension, and ligands) affects device efficiency and stability. Also, we engineer the charge injection/transport layers to achieve better charge balance and suppress the material degradation at the interfaces, which would lead to high efficiency and stability.  

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Research highlight:

[1] H. Cho et al., ACS Nano 2018, 12(3), 2883-2892

[2] H. Cho et al., Advanced Materials 2017, 29(31), 1700579

[3] J. Byun and H. Cho et al., Advanced Materials 2016, 28(34), 7515-7520

[4] Y. Kim and H. Cho et al., Advanced Materials 2015, 27(7), 1248-1254