Introduction of Quantum Dots
LED (light-emitting diode) as one of the lighting and display fields, in recent years, has achieved some rapid development, while the new nanomaterial quantum dots (QDs) show excellent optical properties and have become one of the key development directions in the field of LED technology. Quantum dots refer to the nanometer range particles, and the luminescence of the particles can be controlled by the particle size, which shows broad application prospects in the field of LED lighting and display.
Quantum Dot Products List
Basic Principles and Characteristics of Quantum Dots
Definition and Structure of Quantum Dots
Quantum dots are semiconductor nanocrystals with a diameter ranging from 1 to 10 nanometers. Quantum dots exhibit unique optical properties, and the most direct reason is the quantum confinement effect. By changing the size of the quantum dots, the emission wavelength can be continuously tuned from blue to red, which is the basic reason for the application of quantum dots.
Optical Properties of Quantum Dots
Quantum dots have high fluorescence quantum yield, narrow-band emission spectrum, and good photostability. The luminescence mechanism of quantum dots includes electroluminescence (EL) and photoluminescence (PL), so it can be used in LED and display technology. Quantum dots have high luminous efficiency and narrow-band emission characteristics, which has a huge advantage in the application of LED lighting and display field.
Application and Performance Optimization of Quantum Dots in LED Technology
Quantum dot light-emitting diodes (QD-LEDs) are quantum dot electroluminescent devices. The device structure is composed of an anode, quantum dot layer, and cathode. When a voltage is applied, electrons and holes will be combined in the quantum dot layer to generate photons, so as to realize the emission of light. The structure of QD-LED is similar to OLED. But compared with OLED, it achieves its emission by inserting a layer of quantum dots between the electron and hole transport layers.
Compared with the traditional LED materials in the lighting industry, QD-LED has several advantages, so it has become a very promising alternative material in the LED industry. The first is that the emission color of quantum dots can be controlled by the quantum dot size and material, which can realize color tuning. The second is that the luminous efficiency of quantum dots is close to 100%, which is far higher than the traditional LED material. In addition, quantum dots can be prepared by solution, which is suitable for large-scale production and has low cost. Finally, researchers have also begun to develop non-toxic and non-cadmium based quantum dot materials to reduce its environmental damage.
Optimization of Quantum Dot LEDs Performance
In addition to the above strategies, further improvement of the performance of QD-LEDs is also realized by the following aspects. The first is material optimization. Synthesizing high-quality core-shell quantum dots ((CdSe)ZnS) to improve luminescence efficiency and stability. For instance, continuous progress was made on high brightness and high-efficiency blue QD-LEDs using ZnCdSe core/multi-shell QDs as the emitter. In addition, white light LEDs were fabricated by using the heavy metal-free III-V material (InAs-ZnSe and InP-ZnSeS QDs) and I-III-VI (ZnCuInS/ZnS and CuInS2-ZnS alloys).
The second is the optimization of device structure, which is also an effective means to improve the performance of QD-LEDs. The use of inverted structure and multilayer interface design can improve carrier injection efficiency and light extraction efficiency. For example, further optimization of QD size, the use of different polymers and metal-organic frameworks to adjust its properties, as well as the use of phase separation technique for near infrared (NIR) emission, can also optimize the performance of QD-LEDs. Finally, the surface modification is also an effective approach for improving QD-LED performance. Surface ligand engineering can be used to reduce the nonradiative recombination rate and improve luminescence efficiency. For instance, in the synthesis process, the surface of QDs will be coated with ligands, forming one or more shells. The formed shells can not only protect the QDs, but also make the QDs bond with other materials. In addition, the performance of quantum dot-based LEDs can be further improved by engineering the defect levels and Förster resonance energy transfer mechanism.
