Growing industrial adoption of quantum dot technology by R&D and blue-chip organisations has led to a greater demand for the bulk manufacture of the product. The bulk manufacture of quantum dots provides companies with the platform to develop a wide variety of next-generation products, particularly in application areas such as Displays (Quantum dot display), LED lighting, Backlighting, flexible low-cost solar cells and Biological Imaging.
Since May 2009 the company has been listed on AIM at the London Stock Exchange .
Cadmium Free Quantum Dots
There is a move towards legislation and restriction and in some cases ban heavy metals in products such as IT & telecommunication equipment, Lighting equipment, Electrical & electronic tools, Toys, leisure & sports equipment. In Europe the restricted metals include cadmium, mercury, lead and hexavalent chromium. Maximum concentrations are 0.1% or 1000 ppm for cadmium and for lead 0.01% or 100 ppm by weight of homogeneous material. There are similar regulations in place or soon to be implemented worldwide including China, Korea, Japan, Mexico and the US.
Cadmium and other restricted heavy metals used in conventional quantum dots is of a major concern in commercial applications. For QDs to be commercially viable in many applications they MUST NOT CONTAIN cadmium or other restricted elements Cadmium poisoning. Nanoco has developed a range of restricted metal free quantum dots. These materials show bright emission in the visible and near infra-red region of the spectrum .
The white light LED market is hugely important, with the promise of increased lamp lifetimes and efficiencies paving the way for a revolution in the lighting industry. Color rendering and efficiency are the two most important criteria for traditional light sources for general lighting. The ability of a light source to illuminate an object’s true color is denoted by its color rendering index. For example, sodium lamp street lighting has poor color rendering capability as it’s difficult to distinguish a red car from a yellow car.
Current white light LED technology utilizes a cerium doped YAG:Ce (yttrium aluminium garnet) down-conversion phosphor pumped by a blue (450 nm) LED chip. The combination of blue light from the LED and a broad yellow emission from the YAG phosphor results in white light. Unfortunately, this white light often appears somewhat blue and is often described as “cold” or “cool” white. Quantum dots can be used as LED down-conversion phosphors because they exhibit a broad excitation spectrum and high quantum efficiencies. Furthermore, the wavelength of the emission can be tuned completely across the visible region simply by varying the size of the dot or the type of semiconductor material. As such, they have the potential to be used to generate virtually any color and, more importantly, warm whites strongly desired by the lighting industry.
Additionally, by using a combination of one to three different types of dots with emission wavelengths corresponding to green, yellow, and red it is possible to achieve white lights of different color rendering indexes. Because of these attractive features, QD-LEDs are beginning to receive attention from both industrial and academic researchers. In addition to white lighting for general illumination, there are other opportunities for QD-LEDs. For example, green LEDs are not particularly efficient, thus green-emitting QDs on top of an efficient blue LED chip may be a solution. Similarly, amber LEDs suffer from temperature dependencies and thus a QD solution may be applicable. Furthermore, because of the widely tunable QD emission, it’s possible to have near UV-pumped QD-LEDs with combinations of QDs which emit virtually any color on the chromaticity diagram. This could have important applications in signage by, for example, replacing neon bulbs.
Fabrication of current thin film solar cell technology involves costly evaporation techniques, which is hindering their mass market adoption. CIGS and CIS (copper indium gallium diselenide, copper indium diselenide) nanocrystals or quantum dots allow the use of conventional, low cost printing techniques to fabricate thin film solar cells.
Using the quantum dot method to make CIGS and CIS nanoparticles for photovoltaic applications provide materials which possess the desired elemental ratios or stoichiometry, which can be adjusted to meet specific needs. The material is highly crystalline, mono-dispersed (5.0 nm) particles, which absorb light up to 800 nm.
In this way, the material can be printed onto a substrate using a wide range of printing techniques, even in roll-to-roll processes. Once printed, the CIGS/CIS materials are heated to remove the organic capping agent, which destroys the quantum confinement associated with the QDs and provides for a p-type semiconductor film possessing the desired crystalline structure.
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- Duncan Graham-Rowe: From dots to devices, "Nature Photonics" 3, 307–309 (1 June 2009).