Core Type Quantum Dots

Core Type Quantum Dots

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    Core Type Quantum Dots List

    Quantum dots are semiconductor nanocrystals whose particle size is smaller than the Bohr radius of this material. Due to the unique physical, chemical and luminous properties, quantum dots have attracted much attention. Among them, core type quantum dots are heterogeneous nanocrystals composed of two or more semiconductor materials. On the one hand, core type quantum dots can effectively eliminate the anionic and cationic defects on the surface of mononuclear quantum dots, reducing the non-radiative transition and improving the luminescence performance. On the other hand, the core type quantum dots composed by semiconductor nanocrystals with different properties generally will have new functions. Therefore, in recent years, core type quantum dots have become a research hotspot.

    Applications:

    • Solar cells field: Sensitized nanocrystalline solar cell is a solar cell system that can realize the photoelectric conversion. The most important part of sensitized nanocrystalline solar cell is the photosensitizers, and it can absorb the photonic energy of sunlight. With the advantages of simple preparation and low cost, core type quantum dots are excellent photosensitizers. Based on core type quantum dots, many kinds solar cells can be designed, including quantum-sensitized solar cells, quantum-organic dye hybrid solar cells and the others.
    • An example of core type quantum dots applied in solar cells.Figure 1. An example of core type quantum dots applied in solar cells.

    • The others: Core type quantum dots are also widely used in many other fields, including light-emitting diodes, biomarkers, medical imaging, biosensors and the others.

    Classification:

    According to the arrangement mode, core type quantum dots can be divided into Type-I, Invert Type I and Type-II core type quantum dots.

    • Type-I core type quantum dots: In the structure of Type-I core type quantum dots, the conduction band energy level of shell material is higher than that of core material, and valence band energy level of shell material is lower than that of core material. The typical representatives are CdSe/ZnS, CdSe/CdS and CdS/ZnS. This kind core type quantum dots have high luminescence efficiency and excellent fluorescence stability, and it is favorable for the applications of LED, biomarker, fluorescent probe and the other fields.
    • An example of Type-I core type quantum dots.Figure 2. An example of Type-I core type quantum dots.

    • Invert Type I core type quantum dots: The structure constitute of Invert Type I core type quantum dots is opposite to Type I. The conduction band energy level of shell material is lower than that of core material, while the valence band energy level of shell material is higher than that of nuclear material. The bandgap of core material is greater than that of shell material. In addition, when the core radius or shell thickness of the heterostructure is changed, the limiting range of photocarrier is also changed.
    • Type Ⅱ core type quantum dots: In the structure of TypeⅡcore-shell quantum dots, the position of the core material conduction band and valence band are higher or lower than that of the shell material conduction band and valence band. Compared with the Type I core type quantum dots, the decay period of Type Ⅱ core-shell structure is longer.

    References

    1. Lai L H, Protesescu L, Kovalenko M V, et al. Sensitized solar cells with colloidal PbS–CdS core–shell quantum dots[J]. Physical Chemistry Chemical Physics Pccp, 2013, 16(2):736-742.
    2. Lin W, Niu Y, Meng R, et al. Shell-thickness dependent optical properties of CdSe/CdS core/shell nanocrystals coated with thiol ligands[J]. N ano Research, 2016, 9(001):260-271.
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