Organic Device Technology Breakthroughs to Save Energy

Thankfully, the world is, in part, waking up to energy-shortage and global-warming threats. The two issues are dreadfully linked because, simply, our current choice of fossil-fuel energy generation produces gigantic amounts of greenhouse gases, which, in turn, lead to global warming. Consider, in 2001, worldwide carbon emissions, caused from burning fossil fuel, surpassed 6.5 billion tons, which, according to Washington DC-based Worldwatch Institute, is a fourfold gain in 50 years.

As developing countries in Asia, Eastern Europe and South America are further modernized, global energy consumption could rise 60% over the next 20 years, which will increase our atmosphere’s CO2 concentration to harmful levels – if current methods of energy generation and consumption continue.

Fossil-fuel combustion resulting from human activities accounts for 75% of carbon emissions; the rest comes, largely, from deforestation, which causes the burning and/or cutting of approximately 34 million acres of trees annually, an area equivalent to the size of Italy.

According to Earth Policy Institute (Washington, DC), the largest share of fossil fuel burning comes from: electricity generation (42%); transportation (24%); industrial processes (20%); and residential and commercial uses (14%). Green-solution technologies, such as solar cells and energy-efficient lighting, may solve nearly half the global, carbon-emission problem.

Photovoltaic cells
Presently, conventional semiconductor-type solar cells and LED luminaires show cost effectiveness in certain applications. Researchers believe organic photovoltaic cells (OPVs) and organic, light-emitting diodes (OLEDs) will soon offer substantial cost savings and exciting new applications.

Photovoltaic-cell (PV) construction is based upon thin semiconductor materials, such as silicon or other optoelectronic compounds, which, when struck by light (photons), release electrons that create direct-current (DC). The material, silicon, is most notably used in electronics to either control (diode structure) or amplify (transistor structure) electronic current.

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Currently, PVs use silicon-based photovoltaic material that is both expensive and heavy, and therefore cumbersome for mass-market distribution. However, thinner and lighter OPVs with comparable efficiency and acceptable lifetimes are presently under development.

Traditional silicon PVs operate at 12% efficiency, approximately, and cost roughly $6 per watt output. They’re designed to last more than 25 years. OPVs, presently, endure only a few years with efficiencies ranging near 5%. But, they are lighter, more flexible and may cost less to build.

For commercial viability (and depending on site location and the type of application), an OPV should convert 8 to 10% of the energy it receives (from sunlight) to electricity. Although not there yet, the efficiencies have significantly improved since 1991, when the technology was first demonstrated by Dr. Franz Padinger, the co-founder and chief technology officer of Nanoident Technologies AG (Linz, Austria). At that time, the conversion ratio was less than 1%.

Until recently, OPV efficiency has hovered at 5%, but researchers at Wake Forest University’s (Winston-Salem, NC) Center for Nanotech-nology and Molecular Materials recently exceeded 6% efficiency by incorporating “nano-filaments” within the light-absorbing plastic. Applying the filaments in leaf-vein patterns, the scientists learned, allowed the fabrication of thicker, absorbing layers that captured more light.

Expectedly, several universities, large companies and startups are concentrating on building OPVs, with efficiencies near 10%, to compete with traditional PVs. It’s a matter of improving the material morphology, so it absorbs more light – and of finding ways to improve the system’s overall semiconducting properties. Such upgrades require additional materials or photoactive structures, thus the need for new processing steps that may increase the OPVs’ cost. New processes may also adversely affect the already challenged lifetime that OPVs face.

Despite the challenges, researchers are working on OPVs and hybrids that use plastics and other materials to create flexible or “conformal” devices that can be wrapped around surfaces, rolled up or even painted onto structures. If perfected, such energy-harvesting cells could serve as roof-tile replacements, siding products or building-façade panels. They could also be placed on boats and automobiles. Still, to compete, OPVs’ efficiencies must improve, and they need to be less expensive than their silicon counterparts.

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The most problematic drawback is product lifetime. Certainly, this limitation could prevent OPVs from providing long-term power to buildings, but might allow such niche-market applications as powering shorter-lived devices: signs, hand-held consumer products, satellite gear and RFID tags.

OLEDs
An alarming 22% of all current U.S. energy consumption results from buildings’ interior lighting systems (both residential and commercial) – a high-cost result of utilizing inefficient incandescent and fluorescent lamps. Today’s engineers and chemists are developing carbon-based OLEDs that, soon, may emit a strong white light while operating at the pinnacle of efficiency.

OLED technology is often applied in a matrix structure that may be passive (PMOLEDs) or active (AMOLEDs). Serious lighting and consumer electronic firms are developing PMOLEDs for high-brightness, interior lighting applications. Certain OLED technology has penetrated the display market for backlighting cellphone panels and other small electronic devices – the Sony Walkman and digital cameras, for example. You’ll also find AMOLEDs applications in smaller-sized video displays, with growth plans for sizes that will compete with large-format, LCD and plasma screens.

Recent tests of white-light, OLED prototypes produced by the OLLA Project (Aachen, Germany), using a combination of fluorescent and phosphorescent materials, have demonstrated an efficacy of 25 lm/W and a lifetime of 5,000 hours from an initial brightness of 1,000 cd/m2.

Funded by the European Commission, the OLLA project is a consortium of 24 partners from eight European countries, each a specialist in its particular field of science and technology. OLLA researches and develops high-brightness, highly efficient white OLEDs and demonstrates their use in general lighting applications. The group has formed with the intent “…of propelling Europe to the forefront of OLEDs for display and lighting applications.”

Universal Display Corp. (Ewing, NJ), by doubling the coupling efficiency, has demonstrated a white OLED with an efficacy of 40 lm/W at 1,000 cd/m2. While these are notable improvements for OLEDs in the R&D domain, several companies already make inorganic, semiconductor, white LEDs with efficacies around 50 lm/W in large volumes, at similar or higher brightness, with a projected lifetime exceeding 20 years.

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Indeed, OLED technology needs further improvements, and OLLA has set a goal to soon reach 50 lm/W efficacy, 10,000 hours of lifetime at 1,000 cd/m2 brightness, for a minimum tile size of 15 x 15cm2 by 2008. Such improvements will allow OLEDs to be utilized in the general lighting market and major display markets.

OLEDs are particularly attractive for backlighting such video displays as camera, mobile-telephone, video, computer/laptop and car-navigation screens. According to Philips (Eindhoven, the Netherlands), OLEDs big advantage is the simple manufacturing process and low-cost likelihood.

The OLED (PMOLEDs as well as AMOLEDs) fabrication process requires fewer steps than LCD manufacturing, and, more importantly, fewer materials.

In fact, an entire display can be built on one sheet of glass or plastic, and therefore should cost less to manufacture. Also, unlike LCD and plasma screens, OLEDs and LEDs provide their own light.

OLEDs, with controllable color systems, may eventually illuminate home or office environments. Furthermore, this light source could help achieve governmental, energy-saving goals. In addition to Europe’s OLLA, major lighting and consumer-electronics companies are investing in OLEDs for various lighting and display applications. Other programs include the Next-Generation Lighting Industry Alliance, the U.S. Dept. of Energy’s Energy Star© program and Japan’s Lighting21 energy-savings program.

Without a doubt, you can expect exciting developments in OPV and OLED research and product development over the next few years, especially if strong collaboration extends between the industry’s research and product-development departments. Be aware, however, that announced discoveries and improvements may prove imprecise.

Advancing certain performance areas may degrade others – the overall manufacturability or product lifetime, for example.

Initially, OPV and OLEDs should bring great benefits to niche applications. I believe expanded commercialization will come faster for OLEDs than OPVs; however, integrating the two may offer the ultimate solution, meaning, lighting, display and communication systems powered by the sun.