Quantum dot films in displays

This article is drawn from the IDTechEx Research report Quantum Dot Materials and Technologies 2018-2028: Trends, Markets, Players. This report provides a detailed analysis of QD technology and markets. It provides a ten-year technology roadmap, showing how various QD implementation approaches will rise and fall.

It includes ten-year market forecasts, segmented by QD technologies and applications, showing how the market will grow and how the technology mix will be significantly transformed with time. In terms of displays, it considers edge type, film type, color filter type, on-chip type and emissive type of displays.

This report also provides a thorough technical analysis, outlining many technical (material and device level) and market challenges that must be overcome to commercialise QD technologies. Finally, it provides detailed overviews of the key industry players.

Quantum dots in displays: the story so far

The primary market of quantum dots (QDs) today, beyond research uses, is in displays, Here, the driver is achieving wide color gamut displays thanks to the ultra-narrowband emission of QDs. This attribute is helping position LCDs as a viable competitor against large-sized premium-priced high color quality OLED displays.

Up to now, the QDs’ material characteristics have defined their use case. The QDs have been essentially only integrated into displays as ‘remote’ phosphors. In one implementation, the QDs are loaded into a resin which is then coated onto a film that is then sandwiched by two barrier (encapsulation) layers.

This arrangement is called film-type QD or QD enhancement film (QDEF). In the other implementation, the QDs are put into tubes which are placed at the edge of displays. This is generally called Edge Optic QDs

In both cases, QDs re-emit the light form the phosphor converted backlight LEDs and in doing so narrow the emission spectrum, thus achieving wide colour gamut and thus pushing the display industry further towards the Rec2020 standard.

In both cases, ‘remote’ phosphor integration was adopted because QDs could not tolerate harsher heat or light flux stress conditions which a closer proximity to the light source (LED) would have imposed upon them.

The edge optic QD implementation is now essentially obsolete. Its main proponent (QD Vision) lost an IP battle against the market leader (Nanosys), and consequently had to sell its patent portfolio at a bargain price to a leading QD user (Samsung). The film-type QD implementation however is continuing its growth.

Transition away form Cd based QDs will soon be complete?

Several key trends today characterise the market and technology dynamics of film-type QDs (or QDEFs). Below we will discuss two key trends: transition away from Cd based and reducing implementation cost.

The ban on cadmium (Cd) in Europe is finally announced for October 2019. Even prior to this announcement, Cd QDs had appeared only as a transitory solution, a technology on borrowed time.

To respond, the industry has been developing InP based QDs as an alternative to Cd based ones. In the early days, the performance gap between Cd and InP QD technologies was vast.

Now however, the quantum yield (QY) difference has all but disappeared, whilst the FWHM gap has also been notably narrowed (note: QY affects efficiency and FWHM affects colour gamut).

The FWHM gap however stubbornly persists with InP QDs today achieving around 40nm commercially. Pushing it down towards 38nm commercially (or even 35nm in the lab) remains a challenge.

This is because the emission bandwidth is not just a function of the control of the monodispersity of the QDs during the synthesis, but it is also a function of the shape and crystalline structure of the particles.

Despite this continued performance discrepancy, the market transition appears largely complete. This is shown below: in 2002, the market share of Cd based QDs was nearly. But our report shows, today, in 2018, we expect it to drop to 20%.

Approaches for reducing implementation costs

As with all display components, the pressure to achieve more-for-less is relentless and perennial. QDs are no exception. In case of QD films, it means lowering the cost of entire solution including QD materials, substrate, coating, barrier, etc

In fact, the barrier layers are a significant cost contributer. Their cost however can be lowered if barrier performance requirements are relaxed, leading to simpler barrier film structures. This, in turn, can only be achieved if QD materials become more air stable.

Progress continues to be made here. As our report suggests, the barrier requirements appear to have been relaxed from 1E-4g/day/sqm to 1E-3g/day/sqm and 1E-2g/day/sqm, and now even the target of 1E-1g/day/sqm seems feasible in the near future.

The QD material cost should also be reduced. One way is to increase the efficiency and the brightness of the QDs, leading to a lower consumption per sqm for a given output. Another method would be to lower the cost of QD production per Kg. This of course will stem from greater scale and but also from innovation in the synthesis procedure.