Cadmium-Free Quantum Dot LCD Backlight Films for Medium- and Low-Priced LCD Displays

Improved energy efficient technologies and color gamut are in demand by the display industry. The LCD display market is experiencing the beginning of a new era due to the introduction of quantum dot enhanced TVs in Ultra High Definition TVs. New material developments could help to bring the quantum dot technology to an industrial break through.

More than 99% of the 200mio LCD TVs sold at a global level aimed for the old Rec. 709 standard (high definition TV, HDTV). The new Ultra High Definition TV (UHDTV) is in need of a firmly expanded color gamut as described in Rec. 2020. Thereby, HDTV (Rec. 709) covers only 50% of Rec. 2020. So the new standard is a major leap in display quality.

Quantum Dot Technology Enabling Rec. 2020 in LCD Displays

Quantum Dots (QDs) used in LCD backlight films are considered to be the most feasible technology that helps meet the demands of Rec. 2020. The current generations of UHDTVs use the latest QDs, which are based on cadmium selenides (CdSe) or indium phosphide (InP). These two materials are very expensive in the production and fall in the range of several 10’000USD/kg. Currently, the CdSe-based technology depends on a disputable RoHS exemption while using cadmium. This has increased the interest of InP quantum dots.

It should be noted that indium has limited availability, and InP QDs have a mediocre performance containing low photoluminescent quantum yield (PLQY < 60%) and minimal Rec. 2020 coverage (< 70%). This quantum yield is assigned to a broad emission peak width. A cadmium-free, fully RoHS compliant technology with both great image quality (high Rec. 2020 coverage) and low energy consumption (high quantum yield) would be an unprecedented achievement in the field.

Cadmium-free QDs with Exceptional Color Gamut for Medium-Priced LCD Displays

Recently, an inexpensive and patent protected process to create Cd-free QDs was developed by Avantama®. These Cd-free QDs showed high PLQY of > 90% in dispersion (Figure 1 This high efficiency results in a high energy saving potential matching the CdSe technology without the use of cadmium.

Figure 1. Cost-efficient cesium lead halide quantum dots with high photoluminescence

Figure 2 shows the proprietary cesium lead halide QDs, which are capable of being readily incorporated into an LCD backlight film attaining full RoHS compliance in addition to exhibiting superior cost potential. Avantama has already scaled up the production of the newly formed cesium lead halide QDs to an industrial scale, and the price estimations clearly highlight an advantage over InP or CdSe.

Figure 2. Transmission electron microscopy image of cesium lead halide QDs.

Avantama’s unique backlight film (Figure 3) highlights a high efficiency of > 80% and peak widths measuring as low as 20nm and increasing the functioning of commercial InP backlight films. Figure 4 shows the peaks in the innovative Avantama backlight films that are unique with a narrow peak. Cesium lead halide backlight films have already been used in place of the commercial CdSe film in the fabrication of demonstrators.

Figure 3. Avantama’s proprietary QD backlight film emitting light in response to excitation by blue light

Figure 4. Spectrum of Avantama® (left) and InP (right) backlight film upon excitation by a blue backlight unit of an LCD TV. Avantama’s backlight film shows distinct, narrow green and red emission peaks.

Expansion of UHDTV to Mid-Range LCD Displays

Figure 5 shows by a patented architecture of the backlight film featuring separated green and red QD layers. The new backlight film technology could help expand the addressable LCD display market to low-priced LCD or medium displays as result of the reduction in the fabrication costs when compared to InP- and CdSe-based backlight films.

Figure 5. Cost-efficient, proprietary quantum dot based LCD backlight film with high photoluminescence

Avantama® technology is a suitable replacement to current products, thanks to its RoHS compliance, cost-efficiency, and extraordinary optical performance (Table 1).

Table 1. Comparison of different QD backlight films.

3M Samsung Avantama
Used in Kindle Fire HDX 7 SUHD TV -
QD composition CdSe InP CsPbX3 (X=Br, Cl, I)
total PLQY ~ 80% < 60% ~ 85%
FWHM (nm) ~ 35 (green and red) ~ 40 (green)
~ 50 (red)
~ 20 (green)
~ 35 (red)
Peak position 543 nm
605 nm
530 nm
632 nm
517 nm
636 nm
RoHS compliance Not fully (RoHS exemption) Yes Yes
Color gamut high Limited high
Energy saving potential high Limited high

Conclusion

New varieties of quantum dots provide new materials along with less manufacturing costs, thus enabling the production of cost-effective UHDTVs that are brighter and a lot more colorful.

Avantama has expertise in both nanotechnology and printing techniques and also a comprehensive product range of inks and optical coatings, which will be essential to the manufacture of the next generation UHDTVs.

The range of new products that are possible using Avantama QD materials could make a fundamental difference on the dynamics between LCD technology and new technologies like OLED.

This information has been sourced, reviewed and adapted from materials provided by Avantama Ltd - Nanoparticle Dispersions.

For more information on this source, please visit Avantama Ltd - Nanoparticle Dispersions.

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