Category Archives: LEDs

Fremont, Calif., October 29, 2015 – Soraa, a leader in the development of advanced lighting products and gallium nitride on gallium nitride (GaN on GaN™) LED technology, announced today that it will open a new semiconductor fabrication plant in Syracuse, New York. In partnership with the State of New York, the company will construct a new state-of-the-art GaN on GaN LED fabrication facility that will employ hundreds of workers. Working in coordination with SUNY College of Nanoscale Science and Engineering (SUNY Poly CNSE), the new facility is on pace for shell completion by the end of this year with production beginning in the second half of 2016. Soraa currently operates an LED fabrication plant in Fremont, California, one of only a few in the United States.

“Central New York’s economic growth is due in large part to high-tech companies like Soraa that recognize the region’s wealth of assets and resources,” Governor Cuomo said. “Today’s announcement not only means economic stability for the region, but it also strengthens Central New York as leader in the development of the clean technology that will help light and power the future.”

“Syracuse is an optimal location for the new fabrication facility for a number of reasons including the innovative high-tech vision and strategy of Governor Cuomo; the ability to attract some of the best and brightest scientists and engineers in the world; and the capacity to tightly control the product quality and intellectual property around our lighting products through our partnership with SUNY Poly CNSE,” commented Jeff Parker, CEO of Soraa. “Since we launched our first product in 2012, global market reception for our high quality of light LED products has been phenomenal and sales have soared. The new facility will significantly increase our manufacturing capacity to meet this growing demand.”

It was announced in late 2013 that Soraa would expand its manufacturing operations to the Riverbend Commerce Park in Buffalo, NY. The plans outlined sharing the space with solar module manufacturer, Silevo. However, following the acquisition of Silevo by SolarCity, the facilities at Riverbend could no longer accommodate both Soraa’s fabrication facility and the necessary square footage for SolarCity’s expanded operations. As a result, it was back to the drawing board.

“Following the change with the Riverbend space, we remained focused on finding an optimal solution that worked for the State, Soraa and the talented workers that call upstate New York home,” added Parker. “We’re back on track with a great location and are targeting to employ at least 300 people to support a revenue stream of over $1 billion once fully functional.”

“By taking Albany’s nanotechnology-based public-private economic development model across New York State, Governor Andrew Cuomo has established an unmatched engine for long-term growth, and this latest announcement is a perfect example of how his jobs-focused strategy continues to pay dividends,” said Dr. Alain E. Kaloyeros, President and CEO of SUNY Poly. “SUNY Poly is thrilled to partner with Soraa to locate this advanced manufacturing facility and its resultant jobs, as well as the hands-on educational offerings that this will present for New York’s students, adjacent to the Film Hub in Syracuse, where the company’s cutting edge lighting technology can be adapted for production purposes. Each component of this collaboration is further proof that the Governor’s unique vision for crafting commercialization and manufacturing-based opportunities is a powerful recipe for a resurgent New York.”

In 2007, a team of pioneering professors from the worlds of engineering and semiconductors—Dr. Shuji Nakamura, Nobel Laureate and inventor of the blue laser and LED; Dr. Steven DenBaars, founder of Nitres; and Dr. James Speck of U.C. Santa Barbara’s College of Engineering—came together and made a bet on an LED technology platform completely different than current industry practice, a technology most industry experts at the time considered to be impossible to execute.

Soraa bet that GaN on GaN LEDs would produce more light per area of LED, be of higher quality, and be more cost-effective than technology based on other foreign substrates like sapphire or silicon carbide. This strategy ran against every trend in the LED industry. That bet paid off: today, the company’s LEDs emit more light per LED material than any other LED; handle more electric current per area than any other LED; and the company’s products produce best-in-class color quality with full spectrum light similar to sun-light, while also delivering the brightest beams.

Berkeley, CA, October 29, 2015 — Pixelligent, a leader in high-index materials, announced today the development of a new OLED light extraction technology that dramatically increases light output in their customer’s OLED Lighting devices. Pixelligent founder and chief technology officer, Dr. Gregory Cooper, presented the new technology at the 17th Annual OLEDs World Summit.

These new nanocomposite materials, which combine scattering particles along with PixClear® zirconia, are delivering significant improvements in light extraction and efficiency for numerous OLED lighting applications. “This class of materials represents the next generation of Pixelligent’s technology development strategy. In fact, we have seen light output double in devices that our partners and customers have tested with our PixClear® OLED products,” said Pixelligent Founder & CTO, Gregory Cooper.

Dr. Cooper’s presentation at the conference included the numerous breakthroughs Pixelligent has achieved in OLED lighting applications, derived from its proprietary light extraction nanocomposite materials. These new OLED materials will enable Pixelligent’s customers to deliver new OLED Lighting devices with unprecedented light extraction and cost efficiencies.

 

According to a report from IC Insights, the worldwide market for optoelectronics, sensors and actuators, and discrete semiconductors (O-S-D) has turned into a mixed bag of double-digit growth for several major product categories (lamp devices, infrared circuits, and CMOS image sensors) combined with single-digit declines in sales for nearly a dozen other categories (including most sensors, diodes, rectifiers, and power transistors). Combined revenues for O-S-D products are expected to grow 3% in 2015 to a new record-high $66.4 billion from the current peak of $64.4 billion set in 2014, when sales increased by 9%  (Figure 1). With integrated circuit sales on track to decline by 1% this year, the marketshare of O-S-D products is projected to reach nearly 19% of total semiconductor revenues in 2015, which are now expected to drop by less than a half percent to $354.1 billion.

Figure 1

Figure 1

IC Insights expects growth in the sensor/actuator market segment to slightly strengthen in 2016 with revenues projected to rise 4% to $10.5 billion after increasing just 2% in 2015 to $10.1 billion due to significant price erosion in many sensor product categories.  The commodity-filled discretes segment is expected to recover and grow 3% in 2016 to $22.2 billion after being knocked down 6% in 2015 to $21.5 billion because of a slowdown in equipment manufacturing and weakness in the global economy during the second half of this year.

Optoelectronics is expected to continue to be the strongest growing segment in the O-S-D marketplace during the second half of this decade, primarily because of increasing demand for CMOS image sensors in a wide range of embedded applications (such as automotive, medical, video-surveillance networks, and image recognition systems) along with the spread of solid-state lighting products built with high-brightness light-emitting diodes (LEDs), and the need for more laser transmitters in high-speed optical communication networks.

The other two O-S-D segments — sensors/actuators and discretes — have struggled to maintain consistent growth after rebounding in 2014 from slumps in 2012 and 2013. Discretes semiconductor sales continue to be whipsawed by volatility in product purchases, which have quickly switched on or off depending upon changes in the economic outlook or end-use market demand. Power transistors, which account for more than half of discrete sales, have also seen tremendous swings in demand since 2010.

Additional information regarding market growth trends for optoelectronics, sensors/actuators, and discretes is provided in the October Update to The McClean Report—A Complete Analysis and Forecast of the Integrated Circuit Industry. Expanded coverage and detailed analysis of trends and growth rates in the optoelectronics, sensors/actuators, and discretes market segments is offered in IC Insights’ O-S-D Report—A Market Analysis and Forecast for Optoelectronics, Sensors/Actuators, and Discretes.

Tokyo, October 28, 2015 — Toshiba Corp. said Wednesday that it will retreat from the complementary metal oxide semiconductor, or CMOS, image sensor business, by selling the production line at its Oita plant to Sony Corp.

Toshiba plans to sell the CMOS sensor production facility by the March 31 end of fiscal 2015 at an estimated price of 20 billion yen. Some 1,100 employees from the image sensor business will be rehired by the Sony group.

Toshiba also announced its withdrawal during fiscal 2015 from the white light-emitting diode business as part of reforms of its discrete semiconductor chip operations.

Intensifying competition led Toshiba to suffer market share declines and losses in the image sensor and white LED businesses. The company believes that loss-making operations were a cause of its accounting scandal and aims to accelerate its business reconstruction efforts by reforming semiconductor operations.

The company will set up a new firm in April to integrate the Oita plant in southwestern Japan with Iwate Toshiba Electronics Co., a group firm based in Kitakami in northeastern Japan. The integration is aimed at boosting production efficiency for such large-scale integration chips as analog integrated circuits for in-vehicle devices.

Toshiba will not close the Oita plant and will keep operating five plants in Japan for its production of LSI and discrete chips.

For the reform of semiconductor chip operations, Toshiba will face a surplus workforce of some 1,200 employees who are not moving to Sony. It will seek early retirements and consider transfers to the Yokkaichi plant, a core facility making flash memory chips, and other factories.

The company aims to restore profitability in LSI and discrete chip operations in fiscal 2016 by cutting their fixed costs by about 26 billion yen from fiscal 2014.

According to a new market report published by Transparency Market Research “LED Driver and Chipset Market – Global Industry Analysis, Trend, Size, Share and Forecast, 2015 – 2021“, the global LED Driver and Chipset market was valued at US$2.80 billion in 2014 and is expected to reach US$11.99 billion by 2021, growing at a CAGR of 23.2% from 2015 to 2021.

The global LED Driver and Chipset market is primarily driven by increasing demand among the consumers for efficient power solution both in terms of display and lighting. LEDs outperform the traditional Cold Cathode Fluorescent Lamps (CCFLs) and Liquid Crystal Displays (LCDs) in term of size, energy efficiency, reliability and mechanical ruggedness both for displays and lighting applications. LEDs generate 100% of the National Television System Committee (NTSC) colors plus some extra colors in comparison with LCDs which generates only 70-80% of the NTSC colors. In addition, the operating cost of LEDs is low as compared to other lighting and display devices as LEDs produce more lumen per watt. Thus, more consumers are inclining towards the usage of LEDs which in turn is driving the growth of LED drivers and chipset market. Moreover, increasing awareness among the consumers regarding carbon footprints is also expected to fuel the demand of eco friendly LED devices which in turn is expected to boost the demand of LED Drivers and Chipsets offered by different LED product’s manufacturers. LEDs result in less carbon dioxide and Sulphur oxide emission (451 pound/ year) and help to keep the environment pollution free. Moreover, LEDs produces 90% less heat than incandescent and. CCFL bulbs.

The LED Driver and Chipset market is segmented on the basis of application and geography. The application segment is further bifurcated into display and lighting. By display, LED Driver and Chipset market is classified into: mobile phones, digital camera, television and navigation devices, medical devices, computer/laptop peripherals and others. Gaming devices, digital photo frames and MP3 players are included in the others segment. By lighting, the market can be segmented into outdoor areas and traffic signals, automotives, indoor lighting and commercial lighting among others. Geographically, the LED Driver and Chipset market has been segmented into North America, Europe, Asia-Pacific and Rest of the World (ROW).

Among the different applications, lighting segment was the fastest growing market in 2014. The market is predicted to grow at a CAGR of 24.1% from 2015 to 2021 and accounted for 20.1% of the overall revenue share of LED Driver and Chipset market. By geography, Asia Pacific held the largest market share and is expected to be the fastest growing market expanding at a CAGR of 23.4%. Asia Pacific is mainly driven by China and Japan. The government in this region has taken several steps to phase out the usage of conventional lighting and display technology to reduce carbon footprints. This in turn is expected to increases the sale of LED appliances and is predicted to drive the growth of LED Driver and Chipset market during the forecast period. Advanced Analogic Technologies Inc, Diodes Inc, Exar Corp and Ixys Corp among others are some of the major players operating in LED Driver and Chipset market.

by Dr. Guillaume Chansin, Senior Technology Analyst, IDTechEx

Quantum dots have been developed since the early 80’s but it is only recently that they made an appearance in consumer products such as TVs and tablet computers. IDTechEx Research has published a new market report on quantum dots titled “Quantum Dots 2016-2026: Applications, Markets, Manufacturers”, and as part of this study we have looked at their impact on the display industry. Is this the technology that will enable LCD to rival OLED?

Expanding color gamut

The key selling point for quantum dots is that they enable a much wider color gamut with minimal re-engineering of the LCD panels. They do this by modifying the backlight (and to some extent the color filters) inside the LCD stack.

A conventional LCD backlight uses ‘white LEDs’ which are really blue LEDs with a yellow phosphor. As a result, the white light that is produced has a strong blue peak and much weaker red and green components.

Quantum dots can be used as “downconverters”, the same way that phosphors convert blue wavelength to longer wavelengths. They key difference is that quantum dots have very narrow emission spectra and the wavelength can be tuned by changing the size of the dots. In other words, with quantum dots it is possible to have strong emission peaks in all three primaries: red, blue, and green.

The ideal solution would be to deposit the quantum dots directly on the LED (“on-chip”). But the current generation of materials degrade quickly at high temperature so they need to be physically separated from the chip (future generation materials may enable ‘on-chip’ thanks to high heat and moisture resistance).

Two workarounds are currently available. The first one is to place a tube filled with quantum dots between the LEDs and the light guide plate. QD Vision is the company commercializing this solution. While the tube can be fitted in large displays, it is not the best solution when it comes to mobile displays. The picture below shows an iMac retrofitted with a tube by QD Vision.

Source: IDTechEx Research.

Source: IDTechEx Research.

Back in 2013, QD Vision partnered with Sony to launch the first quantum dot LCD TV. QD Vision has now found more partners, including TCL launching a range of TVs and Philips commercializing the first quantum dot monitor this year.

The other integration option is to add the quantum dots as a film, an approach designed by Nanosys. The company has partnered with 3M to offer a diffuser sheet loaded with quantum dots. Because the diffuser sheet is part of a conventional backlight anyway, the display manufacturers do not need to change anything in the design of the backlight: the 3M solution is a direct drop-in replacement. Amazon was the first customer when it launched tablets with premium displays (the Kindle HDX).

The cadmium question

Quantum dots appear to offer a simple way to dramatically improve the performance of LCD panels. But there are some challenges to get the technology adopted.

First, the cost. A quantum dot film can add a significant cost to the display panel. Using tubes from QD Vision is probably more cost effective which is probably why several Chinese TV manufacturers are adopting this solution.

Second, consumers will have to be convinced that it will be worth paying a premium. Supporters of quantum dots say that it is currently the only way to obtain TV displays that are compliant with the Rec. 2020 standard. But while the specifications are impressive, it is worth noting that most consumers are not aware of the limitations of their existing LCD devices (whether TV, laptop, or tablet).

Third, the best quantum dots are made with Cadmium, an element which is usually banned in the European Union under the RoHS regulations. QD Vision and 3M have requested an exception to introduce cadmium in TVs because of the benefits in terms of lower energy consumption (thereby reducing carbon emissions). But some organizations, including Nanoco, are calling for the exception to not be extended. Nanoco supplies indium based quantum dots so would benefit from a complete ban on cadmium. Some are quick to retort that Indium is a potential carcinogen and might also be banned in the future.

While this debate is much needed to fully assess the risks, there is no denying it has also been damaging to the whole industry. Giving quantum dots a bad reputation is not the best way to get the technology widely accepted.

Nanoco has licensed their cadmium-free quantum dots to Dow Chemicals. But the optical performance of these quantum dots is not on par with the ones made with cadmium. The company believes that eventually they will be able to offer a similar level of performance. Meanwhile, Nanosys has also started to produce cadmium-free quantum dots and has licensed their technology to Samsung.

QLED as the next generation OLED?

While the main focus is currently on enhancing backlights for LCD panels, some are already looking beyond. Quantum dots can also be used to make emissive displays. So-called quantum dot LED (QLED) are similar to OLED with an active layer made with quantum dots.

Market forecast for quantum dot devices and components (Source: IDTechEx report “Quantum Dots 2016-2026: Applications, Markets, Manufacturers”)

Market forecast for quantum dot devices and components (Source: IDTechEx report “Quantum Dots 2016-2026: Applications, Markets, Manufacturers”)

This technology is still in very early stage but promises to offer the same benefits in terms of color gamut to OLED technology. QLED will in theory provide better colors and efficiency than OLED because of the narrower emission peaks. QLED can be considered as the next generation OLED.

Whether it is for downconversion or ultimately QLED, quantum dots have the potential to significantly disrupt the display industry. IDTechEx Research forecasts that quantum dots will enables a market of devices and components worth over $11bn by 2026, with a large chunk of the revenues in display applications. Quantum dots have already made serious inroads in the industry; don’t be surprised to find them in your next TV. For more information, read the full global analysis of the technology and application landscape in the report “Quantum Dots 2016-2026: Applications, Markets, Manufacturers” at www.IDTechEx.com/qd.

Orlando, FLorida – At the Meeting of the International Microelectronics Assembly and Packaging Society (IMAPS 2015), imec and CMST (imec’s associated lab at Ghent University) present a novel technology for thermoplastically deformable electronics enabling low-cost 2.5D free-form rigid electronic objects. The technology is under evaluation in Philips LED lamp carriers, a downlight luminaire and a omnidirectional lightsource, to demonstrate the potential of this technology in innovative lighting applications.

Miniature LED dome test vehicle with integrated low power LEDs. (a) Device before forming. (b) Device after vacuum forming using a 40 mm half sphere.

Miniature LED dome test vehicle with integrated low power LEDs. (a) Device before forming. (b) Device after vacuum forming using a 40 mm half sphere.

Thanks to its energy-efficiency, excellent light quality, and high output power, light emitting diode (LED) technology is becoming the sustainable light source for the 21st century. But in addition, it also allows to design unprecedented, innovative lighting solutions. Imec and CMST’s new thermoplastically deformable electronic circuits now add a new dimension to the possibilities to fabricate novel lamp designs as well as smart applications in ambient intelligence and wearables.

The innovative technology is based on meander-shaped interconnects, a robust technique to realize dynamically stretchable elastic electronic circuits including LEDs. These are then embedded in thermoplastic polymers (e.g. polycarbonate). Following production on a flat substrate, using standard printed circuit board production equipment, the circuit is given its final form using thermoforming techniques such as vacuum forming, high pressure forming or even injection molding. Upon cooling, the thermoplastic retains its shape without inducing large internal stresses in the circuits. The method, based on standard available production processes, does not require large investments, reducing the cost of fabrication. The resulting designs have a low weight and low complexity, a high resilience, a low tooling and material cost, and a higher degree of manufacturer independence due to the standard industrial practices that are used.

The production process was developed in collaboration between the industrial and academic partners involved in the FP7 project TERASEL: imec, CMST (Ghent University), ACB, Holst Centre, Niebling Formtechnologie; Sintex NP and Philips Lighting BV. TERASEL is a European effort focusing on the development, industrial implementation and application of large-area, cost-effective, randomly shaped electronics and sensor circuit technologies.

When University of Oregon associate professor Ramesh Jasti began making tiny organic circular structures using carbon atoms, the idea was to improve carbon nanotubes being developed for use in electronics or optical devices. He quickly realized, however, that his technique might also roll solo.

In a new paper, Jasti and five University of Oregon colleagues show that his nanohoops — known chemically as cycloparaphenylenes — can be made using a variety of atoms, not just those from carbon. They envision these circular structures, which efficiently absorb and distribute energy, finding a place in solar cells, organic light-emitting diodes, or as new sensors or probes for medicine.

Though barely one-nanometer, nanohoops offer a new class of structures for use in energy or light devices. (Courtesy of Ramesh Jasti)

Though barely one-nanometer, nanohoops offer a new class of structures for use in energy or light devices. (Courtesy of Ramesh Jasti)

The research, led by Jasti’s doctoral student Evan R. Darzi, was described in a paper placed online ahead of print in ACS Central Science, a journal of the American Chemical Society. The paper is a proof-of-principle for the process, which will have to wait for additional research to be completed before the full impact of these new nanohoops can be realized, Jasti said.

These barely one-nanometer nanohoops offer a new class of structures — sized between those made with long-chained polymers and small, low-weight molecules — for use in energy or light devices, said Jasti, who was the first scientist to synthesize these types of molecules in 2008 as a postdoctoral fellow at the Molecular Foundry at the Lawrence Berkeley National Laboratory.

“These structures add to the toolbox and provide a new way to make organic electronic materials,” Jasti said. “Cyclic compounds can behave like they are hundreds of units long, like polymers, but be only six to eight units around. We show that by adding non-carbon atoms, we are able to move the optical and electronic properties around.”

Nanohoops help solve challenges related to materials with controllable band gaps — the energies that lie between valance and conduction bands and is vital for designing organic semiconductors. Currently long materials such as those based on polymers work best.

“If you can control the band gap, then you can control the color of light that is emitted, for example,” Jasti said. “In an electronic device, you also need to match the energy levels to the electrodes. In photovoltaics, the sunlight you want to capture has to match that gap to increase efficiency and enhance the ability to line up various components in optimal ways. These things all rely on the energy levels of the molecules. We found that the smaller we make nanohoops, the smaller the gap.”

To prove their approach could work, Darzi synthesized a variety of nanohoops using both carbon and nitrogen atoms to explore their behavior. “What we show is that the charged nitrogen makes a nanohoop an acceptor of electrons, and the other part becomes a donator of electrons,” Jasti said.

“The addition of other elements like nitrogen gives us another way to manipulate the energy levels, in addition to the nanohoop size. We’ve now shown that the nanohoop properties can be easily manipulated and, therefore, these molecules represent a new class of organic semiconductors — similar to conductive polymers that won the Nobel Prize in 2000,” he said. “With nanohoops, you can bind other things in the middle of the hoop, essentially doping them to change properties or perhaps sense an analyte that allows on-off switching.”

His early work making nanohoop compounds was carbon-based, with the idea of making them different diameters and then combining them, but his group kept seeing unique and unexpected electronic and optical properties.

Jasti, winner of a National Science Foundation Career Award in 2013, brought his research from Boston University to the UO’s Department of Chemistry and Biochemistry in 2014. He said the solar cell research being done by his colleagues in the Materials Science Institute, of which he is a member, was an important factor in his decision to move to the UO.

“We haven’t gotten very far into the application of this,” he said. “We’re looking at that now. What we were able to see is that we can easily manipulate the energy levels of the structure, and now we know how to exchange any atom at any position along the loop. That is the key discovery, and it could be useful for all kinds of semiconductor applications.”

Co-authors with Darzi and Jasti were: former BU doctoral student Elizabeth S. Hirst, who now is a postdoctoral fellow at the U.S. Army Natick Soldier Research, Development and Engineering Center; UO doctoral student Christopher D. Weber; Lev N. Zakharov, director of X-ray crystallography in the UO’s Advanced Materials Characterization in Oregon center; and Mark C. Lonergan, a professor in the Department of Chemistry and Biochemistry.

The NSF (grant CHE-1255219), Department of Energy (DE-SC0012363), Sloan Foundation and Camille and Henry Dreyfus Foundation supported the research.

Applied Materials, Inc. today unveiled two new systems that enable the volume production of high-resolution, thin and lightweight flexible OLED displays for mobile products and TVs. The Applied AKT-20K (TM) TFE PECVD (thin-film encapsulation; plasma enhanced chemical vapor deposition) and Applied AKT-40K (TM) TFE PECVD tools deliver breakthroughs in materials engineering to deposit thin-film encapsulation barrier layers that are crucial for protecting extremely sensitive OLED devices. These systems allow display makers to replace the rigid insulating front glass on the devices and bring to market bendable and curved displays for a new generation of consumer products.

The vibrant color and low power consumption of OLED displays have driven their rapid adoption in smartphones, with flexible OLED now the fastest growing display segment in the mobile industry. The new TFE systems (20K for 925 x 1500mm and 40K for 1250 x 2200mm) address different display market segments to meet the growing demand for more versatile, thinner and lighter small- and large-area flexible OLEDs.

“The advances in size, resolution, picture quality and form factor creates considerable market opportunities for display makers to bring new flexible products to market,” said Dr. Brian Shieh, vice president and general manager of Applied’s Display Products Group. “Flexible OLEDs must be robust enough to meet the real-life demands of consumers, and the Applied AKT-20K TFE system, already in production, allows panel makers to accelerate the introduction of flexible and curved mobile applications that will change the shape of the screens we use every day.”

Key to the Applied AKT TFE product line is the capability to extend the lifetime of flexible OLEDs by offering diffusion barrier films with very low water and oxygen penetration. These high-performance films, deposited at low temperatures of <100°C, address the susceptibility of OLED material to degrade when exposed to environmental elements. In addition, the systems’ unique vision alignment technology ensures accurate and precise mask positioning and deposition, allowing display manufacturers to eliminate photolithography and etch process steps and reduce production costs.

Richard Friend of the Cavendish Laboratory, at the University of Cambridge and colleagues, have blended poly(9,9-dioctylfluorene) (F8) and a poly(para-phenylenevinylene) (PPV) copolymer known as Super Yellow (SY) and used cesium carbonate in their LED’s negative electrode to minimize quenching and give them ultrahigh efficiency devices.

Balancing the charges in the emissive layer of a polymer light emitting diode (PLED) maximizes light output from the device, the researchers report. Many teams have attempted to achieve perfect charge balance by introducing hole transport layers, that carry the “opposite” of electrons, positive holes, using electron injection layers and tuning polymer blends to improve energy transfer. There is, however, always a trade-off between electronic and optical properties. Friend and his colleagues hoped that PLEDs with ultrahigh luminous efficiency, low operating voltage and reasonably large current density should be possible.

By blending the right polymers at the right levels (in this case 9 parts F8 to 1 part SY), the team has now been able to manipulate how well holes can move, hole-mobility, by exploiting the difference in energy levels, the molecular orbitals, of the polymers. Additionally, they swapped the conventional calcium-aluminum negative electrode, cathode, system for one containing a thin layer of cesium carbonate. This layer allows electrons to be efficiently injected into the LED in order to stimulate light emission.

The team reports an ultrahigh efficiency in their device of approximately 27 candelas per amp. In comparison a device based only on SY rather than the polymer blend lights up to only about 12.5 cd/A. This “excellent performance” for the blended device, the team suggests, arises because of the intrinsic hole trapping nature of the blend system, which they explain is further enhanced by accomplishing a perfect charge balance via efficient electron injection.

“The next step could be further optimization of the performance by varying the thickness of the emissive layer and calcium carbonate,” explains team member Muhammad Umair Hassan. “Our experiments reveal that this optimization is very important.”