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Lead sulphide QDs can be tuned across a wide range of wavelengths, enabling NIR (near infrared) or SWIR (short-wave infrared) sensing. Interestingly, they can be integrated with a silicon ROIC (read-out integrated circuit) to create a hybrid QD-Si NIR/SWIR image sensor. This can potentially give a pathway towards high-res small-pixel silicon-based NIR/SWIR sensors, thus doing away with the need for the heterogeneous hybridization of GaAs sensors with Si ROIC.
The first generation of products is already on the market. A leading consumer electronics company was also active in this area. It had made significant acquisitions and was understood to have commissioned a UK QD supplier to scale up its production. This company has reportedly recently pulled the plug.
The promise of this technology remains strong. The challenges are notable too. Stability is a critical issue. Some QD- or device-level encapsulation will be required. The photostability is even more of an issue. Today, sensors can handle low light-level indoor conditions, but going outdoors in applications, such as automotive, will require further developments and, potentially, breakthroughs.
Furthermore, product optimization will be required. QD supply with high batch-to-batch consistency will be needed. The QD film will need to be cast and probably patterned. The curing is likely to be important to ensure good carrier transport but not the loss of yield due to too much compactness. This will likely require some in- or ex-situ ligand exchange. Nonetheless, this remains an exciting area with a promising roadmap for future development and improvement.
Lighting is a high-volume and promising application. The focus has mainly been on red QDs because an efficient narrowband red at the right wavelength can boost the CRI without compromising efficiency.
The challenge has been to develop QDs with sufficient heat, humidity and light stability to survive conditions close to the LED. It will also be very helpful to render the QD as much of a drop-in solution as possible. This will mean enabling it to be mixed with other color converters, e.g., phosphors, and to be processed using existing tools and procedures.
Today, early products are already on the market. These are probably CD-based and are made stable using a silica shelling procedure. Some have also demonstrated sufficient stability with InP for low light level conditions and remote on-chip phosphors, but these are not yet commercially ready.
Note that on-chip types can also be useful in displays. This is because they could replace the phosphors which are used in today’s LED-lit displays. The challenge here, too, is ensuring good humidity, heat and light stability. In displays, both green and red QDs might be required. To learn more, please see the IDTechEx Report “Quantum Dot Materials and Technologies 2019-2029: Trends, Markets, Players.”
Other (phototherapy, solar, agriculture films, security tagging, etc.)
There are many other applications in the pipeline. Some are positioning QDs as color conversion films targeted to agriculture. The idea here is that the film will modify the sun’s spectrum in a way that will boost growth and yield. Here, there is a debate as to whether narrow or broadband emitter will be best-suited, and the answer is likely to be plant-specific, with no universal one-size-fits-all solution. The first generation of products is close to being launched. These are likely to be based on broadband CIS QDs. Multiple field trials have been conducted to quantitatively demonstrated the RoI and value proposition.
Note that the QD stability challenge, as ever, is present, especially as high sun exposure is expected. The QDs will be put amongst other layers in the film. Nonetheless, additional encapsulation layers may be required. The competition here includes dye-based films and LEDs, e.g., magenta, lights. The former can be lower cost, but its spectrum is linked to chemistry and not particle size. To learn more, please see the IDTechEx Report “Quantum Dot Materials and Technologies 2019-2029: Trends, Markets, Players.”
Another application is in security tagging. Companies are developing broadband graphene or carbon QDs that can be added, in very small traces, to liquids, including petroleum products, to act as liquid-level security taggants. Some are proposing the use of QDs in phototherapy. The idea is to use the QDs to modify the color spectrum to meet a specific medical need. This technology could lead to comfortable, portable and wearable phototherapy solutions. There is still also work on QD solar cells. This, however, remains a difficult value proposition in the medium term, unless there is a major breakthrough.
The QD market is changing. The use in displays is rapidly evolving. These transitions will enable many material innovation opportunities. There are many other non-display applications in the pipeline too. This will sustain a strong market for years to come. To learn more, please see the IDTechEx Report “Quantum Dot Materials and Technologies 2019-2029: Trends, Markets, Players.” This report provides a detailed technology analysis and roadmap. It provides market forecasts, in mass and value, segmented by application. It provides an overview of all the key players in the industry. It also offers a critical assessment of existing and emerging material options, material challenges and material innovation and development opportunities.