Quantum Dots in LCD Before OLED
by: David Barnes
Supply Chain - As you read this, retailers are putting Sony model W009A BRAVIA TV sets on shelves around the USA. We’ll be seeing quantum dots in LCD before OLED for sure. It didn’t look that way a few years back, so I thought it would be interesting to bring us all up-to-date on the industrial and commercial development of quantum dot (QD) technology for display applications.
The basic value proposition of QD technology hasn’t changed for electronics. The small size (5 nm nominal) of the semiconducting particles enables quantum confinement of electrons excited by electromagnetic radiation (light photons). The energy confined, then emitted through fluorescence, depends on the size of the particle, so QD can shift light energy from short wavelengths to long wavelengths. In a classic application, blue light can be down-converted to green or red light depending on the size and mix of particles in the matrix. It is also possible to down-convert invisible, shorter wavelengths in the ultra-violet regime to visible blue, green and red.
Of course, nothing is ever that simple. As covered by Ken Werner in February’s Large Display Report, QD technology faces challenges in high-flux, high-temperature environments. If a lot of light energy is coupled into the optical system, the dot can breakdown (e.g. photo oxidation). If the optical system gets hot, surface traps or permanent structural changes can cause output droop. Such effects were discovered by early attempts to use QD technology for shifting sunlight in solar cells or managing the color-rendering index of solid-state light bulbs. Similar problems arose in initial attempts to shift LED wavelengths at the input to LCD light-guide plates, as Ken described.
There are public safety challenges, also. Prohibitions against Cadmium, a common element in classic II-VI compound semiconductors, are quite strict in Asia or Europe compared with the USA. I think this is why Sony is shipping TV sets using QD-enhanced backlights here rather than keeping them in Japan. Fortunately for all of us, development of water friendly alternatives got a boost from biotech applications in recent years. QD companies are hard at work on alternative semiconducting oxide cores.
All this has attracted significant attention from the venture capital community. Nanoco spun out of Manchester University (UK) in 2001 and obtained about $7.4 million in private equity until going public on 2009. Along the way, it ran into IP conflicts with Nanosys, a 2001 Harvard spin-out. Nanoco was forced to end distribution of Cd-based QD materials through Sigma-Aldrich in the USA, so it concentrated on alternatives.
Meanwhile, Nanosys raised about $117 million in six rounds from 2001 through 2012 and obtained $11 million from the Department of Energy for work on battery technology. Nanosys has been quite diverse in its tech efforts.
QD Vision, a third US start up formed out of graduate work at MIT in 2004, and has raised about $66 million in private equity in addition to several million in government grants. QD Vision focused on OLED applications originally but it refocused on LCD applications in time to become the supplier to Sony this year.
There are other companies, such as Pacific Light Technologies in Oregon, that remain focused on lighting or biotech markets… I will cover some of these in a longer article for Large Display Report readers. For now, here is a diagram of the key industrial, technical and commercial relationships.
Focusing on displays, the big news is industrial scale. QD Vision has solved problems associated with high-flux, high-temp backlights and raised capital to build capacity for light injection materials for Sony’s product.
Nanosys is working with 3M on a different approach: adding color light sheets in backlight trays (a less difficult environment). Ideally, the sheets would include diffuser functions to preserve the parts count but in any event, 3M’s Optical Systems group certainly knows how to serve the LCD industry using its new encapsulation film line.
Not to be left behind, Nanoco has granted Dow Electronic Materials an exclusive license for its QD technologies applied to digital displays and Dow is building capacity for QD optical films in Asia. The supplier hopes its Cadmium-free materials will be more acceptable in Asia than are traditional formulations. Past investments and joint developments by Asian display makers have not resulted in real products… the stealth project by Sony and QD Vision is the only result to date.
Given the extent of industrial development, I expect to see more results soon. OLED TV has not progressed as fast as hoped and LCD makers need extra features to justify UHD prices. This looks like the right time for LCD color gamut to become a key product feature and reason for consumer upgrades. -David Barnes