Have to look at the 8 major trends of LED lighting technology + 23 new material technology development
China's semiconductor lighting industry has achieved breakthrough development in terms of output, output value and technical indicators in recent years. In 2014, the output value of semiconductor light sources and lamps in China was 95 billion yuan, a year-on-year increase of 43.9%. Among them, the export of LED lighting products was 9 billion US dollars, an increase of 50% compared with the same period of last year, and the penetration rate of LED lighting was 20%. In the first half of 2015, LED lighting products increased by approximately 23% year-on-year, and exports from January to May were US$4.08 billion, which was comparable to the same period of last year.
Judging from the latest developments in global semiconductor lighting, the global LED device light efficiency laboratory level has exceeded 300 lm/w, the industrialization level has reached more than 150 lm/w, and the LED lighting efficiency laboratory level has reached 200 lm/w. The US SSL plan aims to adjust the industrialization level of the device's light efficiency to 250lm/w, and the LED lighting efficiency industrialization level reaches 200lm/w. In short, the penetration rate and luminous efficacy of LED lighting products are still far from the theoretical and target values, and there is still a need for major breakthroughs in technology.
LED lighting technology presents eight trends
LED lighting technology involves a wide range, is a combination of multi-disciplinary technology and modern information technology, its development presents eight major technology trends.
The first is to improve the energy efficiency of LED lighting. The entire LED energy efficiency at this stage consists of six parts: internal quantum efficiency, chip light extraction efficiency, packaging efficiency, phosphor excitation efficiency, lamp efficiency, and power supply efficiency. Under certain boundary conditions, the theoretical value is 58%. Currently, the energy efficiency of better lamps and lanterns is only 30%, and there is still a lot of room for advancement. All of the above six items must reach 90% or more, and a technical breakthrough is needed.
The second is to improve the light color quality and color rendering of LED light source: To improve the light color quality of LED light source, it is necessary to use RGB multi-spectrum combination, that is, multi-chip combination or multi-color phosphor combination, to achieve a reasonable distribution of the LED spectrum SPD , but also control the main light color parameters, such as color tolerance, glare, photoelectric blinking and so on. LED light source color rendering characterization is a long-term issue of debate, LED light source can achieve a flexible combination of multi-spectrum, the use of any kind of parameter color rendering characterization, are all defective, the ultimate characterization may be in the form of a spectrum. Some experts also proposed using color gamut index (GAT) and CRI to characterize the reduction of light to color.
Third, innovative technologies for LED lighting: LED light sources and lamps are currently the top priority of the LED lighting industry. Technically, it is necessary to accelerate the innovation of luminaire styling and control functions. Specifically, the appearance of the luminaire is creative in shape, flexible in size, and the amount of light is adjusted as needed. , Flexible color changes, random installation locations, etc.
Fourth, in-depth development and application of intelligent lighting: Intelligent lighting technology features include open, distributed, remote telemetry, compatibility, interactivity, etc., is the depth of integration of lighting technology and information technology. In terms of technology, it involves a wide range of key technologies, such as the interface integration between the light module and the drive power. At present, there is no need to have a unified basic standard. It is necessary to conduct R&D, promotion and application based on actual needs.
Fifth, vigorously expand the LED lighting applications: promote the application of non-visual lighting systems, such as health care, ecological agriculture, LED visible light communication, and infrared LED and UV LED applications, rich in content, application technology is rapidly developing. LED display application technology focuses on the development of high-definition small-pitch display and high-definition flexible display technology to achieve high-definition LED TVs and high-definition foldable, wearable display devices.
Sixth, the research of narrow-spectrum LED devices: narrow spectrum of a single LED can realize the spectral flexibility of combined LED, and can achieve a larger color gamut space in LED display. It is a large application field, and the technology of narrow-spectrum LED devices must be realized. There is a breakthrough in material extension.
Seventh, white light LED devices will gradually turn to RGB combination mode: The use of RGB combination of white light theoretically has a higher light efficiency, and to facilitate the lighting dimming, color adjustment, color rendering, etc., technically to focus on improving the efficacy of green LED light , RGB combination may become the mainstream of general lighting.
Eighth, natural light lighting will be the ultimate goal: With the development of LED multi-spectral lighting, people will pay more attention to energy-saving lighting, health lighting and ecological lighting, using similar solar lighting will be the best choice, namely natural light lighting, using LED Technology can be achieved but many technical issues need to be solved.
LED lighting technology has a lot of room for development. It also needs to further improve the energy efficiency and light quality of the entire lamp. While actively promoting the innovation of lamps and lanterns in the application, it is necessary to continuously expand the application areas such as intelligent lighting, non-visual lighting and high-definition display; in order to achieve the ultimate goal in technology, namely natural light lighting, to provide people with energy-saving, healthy and comfortable lighting surroundings.
Nano-luminous new material technology development
Quantum dot luminescence technology has developed rapidly in recent years and is a new technology line in the field of luminescence.
Quantum dot LEDs: Quantum dots (QDs) are fabricated using nanotechnology. QD particles are generally between 2 nm and 12 nm. Quantum dot emitters consist of luminescent cores, semiconductor shells, and organic ligands, such as luminescent core CdSe (cadmium selenide). ) QD particles, its advantages are: can emit visible light to infrared, stable light, internal quantum efficiency of up to 90%, combined with the LED to produce rich, very bright warm white light.
3D printing QD-LED: Princeton University first demonstrated 3D printed quantum dot LED, the bottom layer is composed of nano silver particles, the top is two indium germanium polymers, the quantum dots are nano-cadmium selenide particles, the shell is zinc sulfide package After the upper and lower electrodes are connected, the cadmium selenide nanoparticles emit different visible light, and the QD-LED is printed on a device having a curved surface, such as a contact lens. The technology will be expanded to 3D printing of other active devices such as MEMS, transistors, and solar cells. Once industrialization will be disruptive innovations.
Ultraviolet (UV) QD-LED: The University of Notre Dame is developing a Gallium Nitride QD whose electron holes penetrate through the tunnel (the phenomenon of electrons penetrating the barrier), not the traditional drift diffusion. Ultraviolet (UV) LEDs have made great progress and are covered in detailed articles.
Quantum dot hybrid LED: The quantum dot organic/organic hybrid light emitting diode is researched by Hiroshima University in Japan. It can emit white light and blue light, and the power supply voltage is 6V. 78% of the effective light emission comes from the silicon quantum dots, which increases the output power density by 350 times. The new LED passes through the solution processing process under normal temperature and pressure, and is known as a new revolution in the lighting system.
Quantum Dots Electrically Excited Blue LED: Taitung University cooperated with Far Eastern University of Science and Technology to research and develop electroluminescent blue light diodes using colloidal quantum dots such as cadmium sulfide and zinc sulfide, which are made of organic-like inorganic materials that are highly reliable and can replace OLEDs in tablets. On the application.
Quantum dot backlight technology: embedded quantum dot backlight, the use of embedded Quantum Dots optical film (QDEF) applied to LCD backlight, quantum dots under the blue LED backlight irradiation, emitting red, green RGB white light. Improve LED luminous efficiency, enhance LCD color saturation, increase the LCD color gamut by 30%, also increase backlight brightness, reduce energy consumption, and has been industrialized. This TV is expected to produce 1.3 million units in 2015 and 18.7 million units in 2018.
The second-generation quantum dot display technology: Two research groups of Zhejiang University have jointly developed and put quantum dots into solution. They have the dual properties of crystals and solutions. In principle, they allow electrons to slow down the "steps" and promote the effective combination of electrons and holes. , greatly enhance the quantum dot LED efficiency, performance and stability, luminous quantum efficiency up to 100%, RGB color rich. Applied to display and lighting to achieve a breakthrough.
Graphene luminescence technology: It has been found that graphene luminescence is a new breakthrough and that third-generation semiconductors can also be grown on graphene substrates.
Graphene Luminescent Light Bulbs: Collaborative research between Columbia University and Seoul National University and other institutes has attached graphene microfilaments to metal electrodes with SiO2 on both sides and suspended on a silicon substrate. The current is heated to over 2500°C, so that bright light is invented, and the temperature of the graphene is not transmitted to the substrate. Using the rebound interference of the light emitting filaments and the silicon substrate, the emitted spectrum can be adjusted, known as the thinnest bulb in the world, and can be applied to optical communication. This technology, such as industrialization, will be a disruptive innovation in lighting.
Graphene LED: Tsinghua University recently announced the use of two kinds of graphene, namely GO and reduced graphene (rGO), to form LED. With the change of applied voltage, the emission wavelength can be changed. There are two kinds of interfaces: A series of discrete energy levels that can be applied to luminescence, sensors, and flexible displays.
SiC+Graphene+GaN Film: Silicon is vaporized on SiC wafers, and the remaining graphene film is securely transferred to a silicon substrate. Direct van der Waals epitaxy method is used on this graphene substrate to grow high quality single sheets. Crystalline GaN films will significantly reduce the cost of semiconductor components. IBM recently announced that it has mastered these technologies and will invest 3 billion U.S. dollars in five years to develop high-frequency transistors, photodetectors, biosensors, and "post-Si era" components on graphene substrates. The first step is to significantly reduce GaN blue light. cost.
Glass Substrate + Graphene + Sputtered GaN: The Tokyo University Rattannet Research Group published a graphene multilayer film on a glass substrate and formed a GaN (AlN+n-GaN) film by pulsed sputtering (PSD). +GaN and InGaN multi-layer structure MQWs+P-GaN). Its advantages: The quality of growing GaN is greatly improved, and RGB three-color combination LEDs can be produced, which greatly reduces the cost. It is also possible to fabricate high-transition transistors (HEMTs) made of GaN. If this technology route is industrialized, it will be a disruptive innovation.
Si+Graphene+Molecular Beam Epitaxy GaN: Spain’s Graphene Company announced that graphene is formed on copper foil by using common chemical vapor deposition (CVD) in cooperation with Ritsumeikan University, MIT, Seoul National University, and Dongguk University of Korea. Directly transferred onto a silicon substrate and then grown on graphene using RF-MBE to grow GaN crystals with hexagonal symmetry growing along the C axis, from the Si(100) surface The grown GaN crystal achieves the highest quality.
The above-mentioned three kinds of graphene substrates grow high-quality GaN technology, and do not use MOCVD equipment. The growth efficiency is high, the cost is low, and the quality is high. In addition to application to light emission and laser light, third generation wide bandgap semiconductors can be developed. This will be a disruptive innovation.
The structure of nano-luminescence is diverse, and here are some typical nano-light emitting structures.
Nanowire LED: Bohr Research Institute research nanowire LED, the nanowire core is GaN material, length is about 2 microns, diameter is about 10-500 nanometers, the surrounding material is InGaN. The light in the diode is determined by the mechanical tension between the two materials. This nanowire can use less energy to provide higher brightness, more energy-efficient, can be used for mobile phones, televisions and many forms of lighting, and is known to change. Future lighting world.
Ultra-thin amorphous dielectric film luminescent material: A light-emitting chip was developed at Texas A&M University, and a dielectric film was formed on a silicon wafer by room-temperature sputtering deposition method, wherein a nanocrystalline layer was provided to increase luminous density in the process Compatible with silicon ICs, the process is simple and new nano-luminescent materials.
3D printing “glossy paper”: Rohinni, Texas, USA uses 3D printing light paper to mix the ink and micro LED on the semiconductor layer and sandwich it between the other two layers. The micro LED has only the size of the red blood cell. When the electrons pass the micro LED, they light the glossy paper, which is called the world's thinnest LED light.
Thinnest LEDs: Researchers at the University of Washington announced that they have developed the world's thinnest LED with a thickness equivalent to 3 atoms. This foldable LED will be used in the future for portable, flexible wearable devices.
Ultra High-Speed LEDs: Duke University of America studied the addition of fluorescent molecules between metal nanocubes and gold films to achieve high-speed LEDs, manufacturing 75 silver nanocubes, and trapped light within them, increasing light intensity through Perse The "Er Effect" has been accelerated and accelerated. Fluorescence molecules emit photons at a speed 1,000 times that of conventional LEDs. They can also be used as single-photon sources for quantum cryptography systems to support secure optical communications.
LED close to sunlight: The InSubria University of Italy uses nanoparticle panels to scatter white LED light sources to obtain light close to sunlight. Using the Raleigh scattering principle, the white LED array is diffused into a "blue sky" effect, or a slight yellow spot is simulated. Sunlight, existing products, good results, can greatly enhance the light color quality.
Ultra-clear and flexible display technology: The use of nanotechnology to make phase change material PCM, can be in two states called GST, crystal and glass, this GST under current pulse, crystal glass cycle can exceed 1 million times / second . Three-layer material structure: conductive glass + GST + conductive glass, each layer is only a few nanometers thick, this technology may produce ultra-thin, ultra-high speed, low energy consumption, high-definition, foldable color display.
Other luminescent materials
White-emitting lasers: The University of Arizona developed a laser that can emit R, G, B, which can be mixed into white light, and can also be used for optical communication, which is 10 to 100 times faster than ordinary LEDs.
Nakamura adopted different technical routes and proposed laser lighting as the third generation of lighting.
Phosphine Luminescent Materials: The Australian National University has found that phosphorous thin layers emit light and can be used as PV and LED.
Organic Light Emitting Diodes (OLEDs): They have entered the field of planar lighting, and some have predicted that they will account for a quarter of the lighting field in the future.
Perovskite LED: Cambridge University, Oxford University and other joint development of calcium titanium LED, the process is simple, low cost, claiming that this LED can be industrialized after 5 years.
The nano-luminous new material technology has made great progress in recent years, especially quantum dots, graphene and nano-luminescence, and they all have pioneering and subversive innovations. They may be new light sources for future lighting. The industry attaches great importance.
The growth of high-quality crystals on graphene substrates, in addition to their application to luminescence and lasers, will greatly promote the development of third-generation wide bandgap semiconductor materials and provide support for the development of high-performance components in the “post-silicon era”.