Nanosys Details the Future of Quantum Dots

June 19, 2017 // By Chris Chinnock
Quantum dot manufacturer Nanosys was at SID DisplayWeek speaking about quantum dots in the Business Conference, presenting papers in the symposium session and showcasing its technology on the exhibit floor while also revealing some future innovation in backroom discussions.

In all, the take away is that quantum dots hold great promise to provide a range of new innovations for displays in the coming years. 

Most of the quantum dots that Nanosys makes today are Cd-based.  These go into films produced by 3M that have shown up in TVs to date.  At last year's SID, Nanosys introduced a hybrid quantum dot solution call Hyperion which uses Cd-based green and a Cd-free red quantum dots to meet the RoHS requirements for heavy metals.  This trend toward Cd-free will continue, so the company is mostly focused on these formulations going forward.

At SID this year, the company showed a modified Hisense TV that contains the new Hyperion quantum dots embedded in a film produced by Hitachi Chemical.  The "photo-enhanced" type of QD display has a spectral performance that is quite good with the green having a Full Width Half Max (FWHM) of 25nm at 520 nm and less than 40nm for the red at 644nm.  When coupled with the blue light at 450nm with a FWHM of 20nm, a display should be able to achieve 94% area coverage of the BT.2020 color gamut.  Hitachi Chemical plans to go to mass production with this film in the second half of 2017, so expect TVs in the market in 2018.

The next step for quantum dots is likely to be their placement in the color filter of an LCD.  Called "photo-emissive" by Nanosys, this means the light from blue backlight will pass through the LCD panel and all the way to the color filters before color conversion.  The big advantage of placing the quantum dots here is a huge increase in optical efficiency as the RGB filter are not discarding two-thirds of the light even with a QD film solution.  Such an advantage may be used to make more power efficient TVs with the same brightness or ones with tons of overhead in terms of peak luminance. 

The other major advantage is a more Lambertian light distribution from the LCD display - one of the weak points of today's LCDs.  And, with the elimination of the cross talk in conventional color filters, the QD-in-colorfilter approach enables a color gamut of 90% of BT.2020 with Cd-free materials.

The placement of the quantum dots in the color filters raises two challenging issues, however.  For one, the second polarizer, which is normally after the color filter, needs to be moved inside the LCD cell because the quantum dots depolarize the light.  Panel and TV makers are working on this solution now.