The gist of it: it’s not clear that Canon has solved one of the main problems with Perovskite-based quantum dot development, the presence of lead, but the company claims to have solved many of the other issues associated with volume manufacturing, and at a much reduced cost.
The Perovskite Value Proposition
Perovskites are a type of material known for their impressive light-emitting properties. They are particularly efficient at converting blue light into red and green light, much like phosphors and quantum dots in current displays. Perovskites, however, exhibit some superior qualities. They show ultra-narrow color purity, outperforming indium phosphide quantum dots, which are commonly used today. They also boast superior light absorption capabilities, meaning they can absorb more light in a shorter pathlength. This characteristic is highly valuable in certain display technologies such as QD-OLED.
The light emission wavelengths of perovskites can be tailored to suit specific needs. Recent research has shown that these materials can allow display manufacturers to achieve a balance between wide color gamut and brightness – often a challenge in the industry. This means, with the help of perovskites, display makers can have higher brightness without sacrificing color gamut, or a wider color gamut without losing brightness.
However, there are still challenges to overcome before perovskites can be widely adopted in the display industry. One of these challenges is stability, as perovskites were originally relatively unstable under conditions necessary for commercialization. But, progress is being made with companies now reporting that they have achieved the necessary lifespan for perovskites to be used in commercial products.
Another major challenge is the fact that perovskites contain lead, a heavy metal restricted by various environmental regulations. There’s ongoing debate about whether the benefits of perovskites can outweigh this drawback. Despite these issues, efforts are being made to reduce lead content while maintaining the exceptional optical properties of perovskites. The question of heavy metals is a significant one, as seen in the quantum dot industry, which has also had to navigate similar challenges.
Perovskite Challenges Faced Head-On by Researchers
An exciting development in the world of perovskites comes from a team of researchers from Seoul National University, the University of Cambridge, Peroled., and the Korea Basic Science Institute. They’ve reported the creation of an ultra-bright, highly efficient, and stable perovskite-based LED.
One of the challenges they tackled involved finding suitable materials for charge transport, an issue exacerbated by incompatibilities between the charge transporting layers and the perovskite deposition processes. To overcome this, the researchers inserted a thin layer of lithium fluoride between the polymer hole transport layer and the perovskite layer. This layer served to secure the structure and minimize non-radiative energy losses in the LED, thus improving its efficiency.
Has Canon Solved the Perovskite Problem?
Canon has just announced the development of a perovskite quantum-dot ink designed for next-generation quantum-dot displays, which it is claimed have successfully demonstrated practical durability. Canon’s perovskite quantum-dot ink is a non-cadmium (Cd) approach to quantum dot technology. Cadmium has been widely used in quantum dots, but due to environmental concerns, industry interest has shifted towards Cd-free materials, as reflected in the previous discussion on the environmental concerns about lead content in perovskites. This represents a key development in the application of perovskites in display technology, marking a significant step forward in creating environmentally friendly, high-performance display materials.
The durability issue, which has previously been highlighted as a significant challenge in the adoption of perovskite-based technology, appears to have been addressed by Canon. They have developed a proprietary technology that forms a protective shell on quantum dots, thereby enhancing the durability of perovskite quantum-dot ink without compromising color purity and light usage efficiency. This supports the previously discussed advancements made in perovskite stability.
Furthermore, Canon’s perovskite quantum-dot inks have shown superior performance compared to indium phosphide (InP) quantum dots. Specifically, Canon’s perovskite quantum-dot inks cover 94% of the color gamut based on the ITU-R BT. 2020 recommendation, as opposed to InP quantum-dot ink’s 88%. This six percentage points improvement indicates that perovskite quantum-dot inks can provide a wider color gamut, thus enhancing the visual expressiveness of displays.
Canon’s perovskite quantum-dot inks are also expected to reduce power consumption of quantum dots by approximately 20% compared to conventional technology, which aligns with the previously discussed superior light absorption properties of perovskites. In addition, they suggest that this new technology could potentially be instrumental in realizing next-generation OLED displays with ultra-high definition, such as quantum-dot 8K displays.
The Toxicity of Quantum Dots
When it comes to toxicity, all three elements considered practical for use in quantum dot materials — cadmium, indium, and lead — can be harmful to humans and the environment when they are improperly managed or when exposure is too high. However, they each have different degrees of toxicity and affect different systems within the body.
Cadmium is highly toxic and can cause serious health problems, including kidney disease, lung damage, cancer, and even death in cases of acute exposure. It’s also harmful to the environment, as it doesn’t break down naturally and can accumulate in the soil and water, causing harm to wildlife.
Lead is also highly toxic, particularly to children. Exposure to even low levels of lead can cause damage over time, especially in children. The greatest risk is to brain development where exposure to lead can cause irreversible harm, including reduced IQ, behavioral issues, and learning disabilities. In adults, lead exposure can cause health problems, including high blood pressure and kidney damage. It’s also harmful to the environment, as it can contaminate soil and water.
Indium, while not as extensively studied as cadmium and lead, has also been shown to have toxic effects on the body, especially the lungs. In one study, workers exposed to indium tin oxide (used in flat-panel displays) were found to have lung damage. However, the toxicity of indium is generally considered to be lower than that of cadmium or lead.
The Health and Safety Standards
The main standard that the display industry is concerned about when it comes to hazardous materials in displays is the Restriction of Hazardous Substances (RoHS) directive. The RoHS directive was adopted by the European Union in 2002 and it aims to restrict the use of hazardous substances in electrical and electronic equipment. The directive has been amended several times since it was adopted, and the current version is the RoHS 2 directive, which was adopted in 2011.
The directive requires that the concentration of lead in all electrical and electronic equipment must not exceed 0.1%. This limit applies to all parts of the equipment, including the display panel. There can be little doubt that the directive has helped to reduce the amount of hazardous substances in electrical and electronic equipment, however, that doesn’t mean there is no pushback.
While there is no doubt about the toxicity of lead, it is not airborne, and in a fully encapsulated display, it should pose no threat, in theory. Also, the material content is very small, the target being less than 0.1% of a product. Cadmium doesn’t stir up the same PR as lead might, maybe due its speciality use, but it is equally harmful and has been used, and while Indium is not toxic as either, it shouldn’t even be considered if you adopt the consensus of other critics of the RoHS standard who think there should be zero tolerance for hazardous materials in electronics.
More importantly, the tolerance for hazardous materials has to go hand-in-hand with the general increase in the manufacturing of green energy products, such as solar cells, which are driving, directly and indirectly, the development of electroluminescent perovskite-based products. It’s not just about displays but the integration of various electronic manufacturing processes in pursuit of cleaner energy and electric vehicles. In other words, there is a lot of research, and investment going into technologies that are going to bleed across clean energy, electric vehicles, and low power displays. It’s hard to see how the issue of toxicity is not resolved at the pace of development and at the scale that we are talking about here.
