Presidential Green Chemistry Challenge: 2014 Greener Reaction Conditions Award
QD Vision, Inc. (technology acquired by Samsung)
Greener Quantum Dot Synthesis for Energy Efficient Display and Lighting Products
Summary of Technology: Most white light sources include a primary light source and a “downshifting” phosphor which converts some or all of the primary light into the desired white light spectrum. In a typical fluorescent bulb, electrified mercury gas produces the primary light in the ultraviolet (UV) range, and phosphors (the whitish powder on the inside of the bulb) convert that UV light into white light. Similarly, today’s light emitting diodes (LEDs) produce a blue primary light, and phosphors convert some of that light to make it appear whiter to the human eye. However, these LED phosphors emit light in a broad band and result in a tradeoff between color quality and efficiency. As a result, display manufacturers must either make displays that cannot show the full range of colors found in nature, or greatly reduce the product’s efficiency. Lower efficiency means that more LEDs are required to achieve the same brightness, and hence cost more to make and need more energy to run.
Semiconductor nanocrystal quantum dot technology offers high-quality color to the solid-state lighting (LED light bulbs) and liquid-crystal display (TVs, mobile devices) markets with high system efficiency. While developing these energy-saving materials, QD Vision also developed a much greener synthesis. QD Vision estimates that they avoid using 150,000 liters (40,000 gallons) of highly toxic solvent per year and avoid 100 kilograms of cadmium waste in production in the United States. QD Vision achieved these improvements by replacing alkyl phosphine- and alkyl phosphine oxide solvents with long-chain hydrocarbons, reducing both the hazard and amount of solvent used. They also replaced highly hazardous organo-cadmium and organo-zinc building blocks with less hazardous precursors. Finally, they improved their purification by switching from centrifugation to filtration saving time and energy, and reducing waste. QD Vision has implemented all of these changes while simultaneously improving material performance. As such, QD Vision quantum dots were the first to be implemented in mainstream commercial devices, including ten different models of Sony TVs in 2013.
Using QD Vision Color IQTM components in 20 million TVs (equivalent to roughly 10 percent market penetration) is projected to save 600,000,000 kilowatt-hours (kWh) of electricity per year worldwide—enough electricity to power 50,000 average U.S. homes. Although QD Vision quantum dots do still use cadmium, the amount of cadmium used in a device is less than the amount of cadmium emissions prevented through reduced electricity production, resulting in a net decrease in cadmium waste.
Podcast on the technology:
2014 Greener Reaction Conditions Award podcast (mp3) (MP3, 1.1 MB, :59 seconds)