Quantum dots: progress, challenges and future in LED lighting: Page 2 of 3

April 10, 2020 //By Dr Khasha Ghaffarzadeh
Quantum dots
First, we must ask what value Quantum Dots (QDs) might deliver in LED lighting? In general lighting, QDs can enable simultaneously higher efficacy and higher CRI (color rendering index) values.

The requirement to create a drop-in solution is also key, especially in shortening time-to-market. This is particularly important because the red QD is to be mixed with other phosphors. As such, it would be hard to imagine a separate mixing and deposition process specific only to the QD.  The current best-in-class technology allows the QDs to be mixed in silicone, applied, and then cured. The QDs will also survive a standard solder reflow process used in mounting the LED packages.
Today, cadmium based QDs are the most stable. In displays, InP has gained significant market share, especially via the Samsung value chain, and has greatly narrowed the quantum yield and FWHM performance gap vs cadmium based QDs.  The InP quantum dots are however not stable enough for on-chip lighting conditions.

The challenge here is that cadmium is toxic. The EU had agreed to ban it starting from last Oct. However a new consultation is now ongoing, which is widely expected to result in a further extension. On the lighting side, the developers argue, with good justification, that no viable alternative yet exists. This argument will likely win time in the short or even medium term. However, it is not a permanent solution, meaning that non-cadmium alternatives with enough stability will be required, pointing towards an urgent innovation and development opportunity.
On the display size, on-chip QD technology can enable the direct integration of the QD into the LEDs used in LCD backlighting, eliminating additional QD films. It is also a frontrunner for micro-LED technology given that unlike standard phosphors, it can meet the size constraints. The QD concentration per LED can be high (<5ug/mm2), but when scaled over the entire display area, it is so high (0.08-0.2ug/mm2). Currently, there is consultation as to the right limit for this use case.


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