In the competitive display market, developers are in a constant race to elevate the user sensory experience – sight being the most important and discerning of the human senses. As a result, manufacturers thrive by adopting innovative technologies that improve display quality. However, prior to adoption, new technologies must prove their reliability and adherence to the stringent manufacturing requirements of the industry.
The implementation of quantum dot technology in displays is a prime example of an on-going disruption making its way to the mainstream market. The technology has advanced a lot in features and has overcome critical reliability and quality control hurdles.
Quantum dots, commonly referred to as ‘QDs’, are nanocrystals (tiny particles about a billionth of a meter in dimension) formed out of semiconductor materials. When illuminated, QDs efficiently absorb photons of light, which excite electron-hole pairs in the material. Within nanoseconds (billionths of a second) of excitation, these pairs 'relax’: recombining to emit light of lower energy than the absorbed illumination. This process is known as “downconversion”.
Due to the quantum confinement electron-hole pairs in a QD, the downconversion process can be precisely dialed to yield a specific wavelength (i.e. color) of light by adjusting the QD’s size. For instance in CdSe – a first generation QD material – a 3 nm (nanometer) QD emits light at a wavelength of 530 nm in the green spectrum, while a 5.5 nm QD emits at a wavelength of 630nm, which corresponds to red.
A few years ago, QDs were introduced to some segments of the LCD display market as an alternative to conventional white LED backlighting. QLED, as that quantum dot display technology came to be known, uses QDs as downconverters that more accurately recreate the RGB colors and, thereby, significantly expand the color gamut of the display.
Despite the manufacturing limitations of the early generations of QDs, the performance improvements observed in those first LCDs with QDs, were promising enough to spur further progress in the implementation of QD technology in displays. Different approaches were implemented or envisioned for augmenting displays with QDs, these include: QD enhancement films (QDEF) and QD color converters in OLEDs. In a nod to the technology’s eminence, Samsung recently announced their intention to expand QDs into OLED displays, in addition to their premium QLED offering .
QD technology is trending not only in displays, but is also penetrating other applications like photodetectors and solar cells. Consequently, demand for QDs has skyrocketed from several kg in 2013 to a few tons presently. New innovations are needed to make quantum technology accessible to the mass market over the next few years.
The problem
QDs emit at a wavelength correlated with their size; and by controlling the QD’s size, the emission can be tuned to a specific color range. However, to get pure colors, i.e. downconversion with a narrow spectrum, requires manufacturing conventional QDs with almost atomic precision.
Conventional types of QDs, like those based on CdSe and InP, are exquisitely sensitive to minute variations in consistency, which may degrade their properties and essentially preclude them from delivering on all their promised benefits for display quality.
Miniscule random variations in reaction or temperature gradients – a normal feature of processing of most materials – lead to considerable fluctuations in the properties of QDs, like color purity and emission efficiency. The fluctuations grow with the scale of the production, creating quality issues beyond the tolerances of display manufacturing standards.
Without innovations in QD technology, the quantum dot display industry faces a shortage of high-quality materials that could deliver a quantum leap in screen color, brightness, and efficiency.
The solution
Recent groundbreaking advances in the composition and nanotechnology tools for the processing of QDs has led to a new generation of quantum materials called perovskites. Perovskite Quantum Dots are more emissive and color pure than those of CdSe and InP; and, notably, their electron-hole pairs are ‘weakly ‘confined (their energies are not as strongly correlated with the nanocrystals’ dimension). As a result, the optical properties of perovskite Quantum Dots can withstand minor variations in sizes and compositions better than previous generations of QDs, whose electron-hole pairs are ‘strongly’ confined within the nanocrystals.
Manufacturers of nanotechnology like Quantum Solutions, a leading developer of third generation QDs, have resolved the long standing issue of scaling up production, without compromising on quality by innovating new processes and compositions that exploit the robust properties of perovskite Quantum Dots.
The new generation of QD technologies, which are based on perovskites, can be produced in commercially large quantities while still maintaining full control over their emission peak and the narrow emission required for high-quality displays. With proper surface “passivation”, they can have luminescence efficiencies close to 100% (almost unheard of in previous compositions).
For instance, QDot™ SharpGreen perovskite Quantum Dots and the QDs polymer films developed by Quantum Solutions for displays offer highly pure colors with luminescence efficiencies close to 100% -- a performance that would not be possible on a commercial scale in other types of QD materials.
Quantum dot technology is changing the future of displays
There are tremendous benefits of using quantum dots in displays. Breakthroughs in compositions and production approaches of QD technologies will be driving improvement in image quality and viewing experience in displays for years to come.