Quantum dots, because they are both photoluminescent and electroluminescent and have unique physical properties, will be at the core of next-generation displays. Compared to organic luminescent materials used in organic light emitting diodes (OLEDs), QD-based materials have purer colors, longer lifetime, lower manufacturing cost, and lower power consumption. Another key advantage is that, because QDs can be deposited on virtually any substrate, you can expect printable and flexible displays of all sizes. To date, the integration of QDs into a full-color LED structure has not been possible due to the difficulty in patterning individual red-green-blue (RGB) QDs onto the pixelated display panel. Now, a Samsung team has demonstrated a novel transfer printing approach which enables fine patterning of high-quality QD films for large-area (4-inch diagonal), full-color displays mounted on glass as well as on flexible plastic substrates.
OLEDs - organic light-emitting diodes - are full of promise for a range of practical applications. OLED technology is based on the phenomenon that certain organic materials emit light when fed by an electric current and it is already used in small electronic device displays in mobile phones, MP3 players, digital cameras, and also some TV screens. With more efficient and cheaper OLED technologies it will possible to make ultra flat, very bright and power-saving OLED televisions, windows that could be used as light source at night, and large-scale organic solar cells. In contrast to regular LEDs, the emissive electroluminescent layer of an OLED consists of a thin-film of organic compounds. Exciton quenching and photon loss processes still limit OLED efficiency and brightness. Organic light-emitting transistors (OLETs) are alternative, planar light sources combining, in the same architecture, the switching mechanism of a thin-film transistor and an electroluminescent device. Thus, OLETs could open a new era in organic optoelectronics and serve as test beds to address general fundamental optoelectronic and photonic issues.
With all the buzz that is being created by portable e-book readers, it's worth taking a look at one of the advanced display technologies - also often referred to as electronic paper - that make these devices happen. Unlike a conventional flat panel display, which uses a power-consuming backlight to illuminate its pixels, electronic paper reflects light like ordinary paper and is capable of holding text and images indefinitely without drawing electricity, while allowing the image to be changed later. Because they can be produced on thin, flexible substrates an due to their paper-like appearance, electrophoretic displays are considered prime examples of the electronic paper category. Electrophoretic displays already are in commercial use, for instance in the Kindle or in the Sony Reader, but so far the displays are mostly black and white. There are still cost and quality issues with color displays. New work by researchers in South Korea shows that organic ink nanoparticles could provide an improved electronic ink fabrication technology resulting in e-paper with high brightness, good contrast ratio, and lower manufacturing cost.
OLEDs - organic light-emitting diodes - are full of promise for a range of practical applications. With more efficient and cheaper OLED technologies it becomes possible to make ultraflat, very bright and power-saving OLED televisions, windows that could be used as light source at night, and large-scale organic solar cells. One of the drawbacks of this technology, apart from its currently high manufacturing cost, are problems with the OLED fabrication process where issues such as material damage, yield, and thickness uniformity haven't been completely solved yet. Researchers in Japan have now proposed a nanoparticle-based deposition method that might be able to overcome these fabrication problems.
In a previous Nanowerk Spotlight we have reported about the work of Chinese scientists who demonstrated that a sheet of carbon nanotube (CNT) thin film could be a practical magnet-free loudspeaker simply by applying an audio frequency current through it . The team has now reported that their CNT films can also work as an incandescent display, driven by a simple addressing circuit with response times faster than that of liquid crystal displays (LCDs). At the same time, the incandescent light of the CNT film is almost nonpolarized, and will not have the viewing-angle problem of LCDs. The CNT films in vacuum can be heated to incandescence and cooled down in about 1 millisecond by turning on and shutting off the heating voltage.
The prospect of stretchable electronics opens some exciting possibilities - for instance, think about artificial skin with an integrated, stretchable touchscreen display. To get there, researchers have begun developing elastic electrical wiring that is both highly conductive and highly stretchable. Currently existing stretchable materials do already exhibit excellent conductivity and mechanical stretchability but they have one major disadvantage: their manufacturing processes are not readily scalable, which means it is difficult or cost-prohibitive to apply them to large-area electronics. A research team in Japan has now successfully fabricated, for the first time, novel elastic conductors that can be directly patterned by printing processes. This novel, printable elastic conductor comprises single-walled carbon nanotubes uniformly dispersed in a highly elastic fluorinated copolymer rubber.
Following up on yesterday's Spotlight about graphene quantum dots, today we look at what might be the first realistic application of this revolutionary material. Back in December we reported on the development of transparent and conductive graphene-based composites for use as window electrodes in solid-state dye sensitized solar cells. While the researchers who conducted this work produced graphene by chemical oxidation of graphite, a multi-step process, new results from the University of Manchester group that discovered graphene in 2004 show a simpler route to producing graphene films that cannot only be used for solar cells but might be well suited for liquid crystal displays.
Many of us don't like to admit it, but televisions are an important part of our lives. Technology has improved the quality and convenience of TVs and has given us a whole new set of choices - high definition, plasma, and liquid crystal displays. With an estimated 66 million sets to be sold this year, flat-screen LCD televisions are the most popular choice. Much of the reason behind the popularity of these high-tech wonders is the decrease in price that happens with most cool technology - a few years after they have been on the market. But, for the popular LCD TV, a shortage of a key compound used to produce LCDs may force manufacturers to raise prices. Electronics suppliers are facing a shortage of the rare metal indium, a co-product of zinc mining. Indium is a rare, malleable and easily fused metal, similar to aluminum, which is used to make indium tin oxide (ITO), the standard transparent electrode used in nearly all flat panel displays and microdisplays. Indium is expensive and scarce and demand is increasing. According to Displaybank, the demand for indium was 861 tons in 2006 and may reach nearly 2000 tons by 2011. Five years ago, indium was about $100/ kg; now it costs $800/kg. Displaybank expects the total sales of indium in 2007 to be $533 million. But, geologists say the cost of indium may not matter soon, because the earth's supply of it could be gone in four years. This could put a serious damper on that 52" LCD screen you've been dreaming about. Fortunately, with the help of nanotechnology, a team of scientists in Japan have developed a new material that may replace the need for indium in LCD production.