Quantum Dots: IDTechEx Research Analyses Changing and Expanding Application Landscape

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Quantum dots (QD) are a successful example of nanotechnology. IDTechEx Research expect that QDs will be used in over 7 Msqm of displays in 2019 (for exact forecasts consult the report). The current dominant method of QD integration in displays is the film-type. This is a non-ideal solution designed as a workaround to current material shortcomings. However, as the QD material system expands, new methods of integration as well as new applications beyond displays will become enabled.

In this article, IDTechEx Research will briefly outline some of the key material development trends. This article will touch on different materials compositions and different applications. This analysis is drawn from the IDTechEx report “Quantum Dot Materials and Technologies 2019-2029: Trends, Markets, Players” (www.IDTechEx.com/QD). This report provides detailed technology analysis of quantum dots, detailed technology roadmaps and timelines, complete overviews of key players in the industry, and market forecasts segmented by 11 application areas at the component as well as material levels. It gives you the complete detailed view of the QD technology, competitive and market landscape.

InP: Successful Successor

The InP chemistry is already a successful commercialized alternative to Cd based QDs. It has significantly narrowed down the FWHM, bringing it to the 38-42nm levels for commercial samples. The rate at which the FWHM is narrowed has however plateaued, and today every nm reduction in FWHM has become challenging, especially in volume production. The quantum yield (QY) has also improved, largely bridging the gap with Cd QDs.

InP QDs however still fall short on multiple parameters. The blue absorbance of the green InP QDs is still too low, by a factor of 2, compared to Cd-based QDs. This complicates efforts to achieve QD color filters (QDCFs). This is because the loading in the resist and/or layer thickness will have to be increased to compensate for this material shortcoming. Improving this is an area of ongoing effort.

Improvement of stability is also an on-going area of development. Today, red Cd-based QDs with silica shelling have reached sufficient heat and photostability to be used on-chip for mid-power LED lighting applications as a near drop-in replacement solution. These red QDs enable boosting lm/W and CRI simultaneously to levels beyond those accessible by current inorganic phosphors. InP QDs, however, are yet to reach this level of stability, suggesting that there is still opportunity for further material development.

Furthermore, champion results suggest that EQE for electroluminescent of red and green Cd-based devices is approaching phosphorescent OLED materials. The EQE of leading InP however is still lagging behind. The red and green have already exceeded 17% and 13%, respectively. However, the best blue is still someway below (champion results are 9% or so). The more critical challenge however is to do with lifetime and luminance. In both fronts, significant development efforts remain.

In general, important material development opportunities exist in QLED (quantum dot LEDs), and not just in the QD itself but in the entire stack of materials. A key challenge is maintaining good charge balance in the device. ZnO and other metal oxide nanoparticles are now commonly reported as a suitable electron transport layers (ETL). However, the research for an optimal hole injection layer continues. In general, it is difficult to find material with sufficiently deep valence bands. Therefore, hole injection lags electron injection, leading to charge imbalance and all the subsequent adverse effects on device performance. The QD material itself is being actively researched. Graded alloyed structure are popular as they eliminate abrupt internal interface, leading to better stability. Better shelling procedures are needed even for red and green QDs. The material composition is also changing, partly to enable between band alignment with the stack materials. The choice of the non-toxic blue material is also still an open question with some companies developing even alternatives to InP QDs targeting high efficiency at the right wavelength (InP currently falls short on the metric).

Clearly there is a long road from demonstration of champion high-performance small-sized spin-coated devices to actually large-sized RGB patterned (e.g., inkjet printed ones). The technology development will take time, even though the industry has extensive accumulated knowhow in the use of inkjet printing in OLED displays for the active materials and the organics in the thin film encapsulation.



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