The reinvention of light

Organic light-emitting diodes (OLEDs) create a world in which illuminated wallpaper and windowpanes that turn into a source of light at night are possible. Experts are convinced that in the next few years, these promising energy savers could revolutionize the lighting sector.

The centuries-old door is three meters high, dark and heavy, allowing no light to pass through. But behind this door, the future of lighting is being developed. This is where Professor Dr. Karl Leo has his office at the Dresden University of Technology, Germany. Together with his team, he is developing a very special lighting panel. The 53-year-old works at the university’s Institute of Applied Photophysics. At the same time, he manages the Fraunhofer Research Institution for Organics, Materials and Electronic Devices (COMEDD) in Dresden and is internationally recognized as a pioneer in the field of organic light-emitting diodes (OLEDs). He and his team are aiming to realize the potential of OLEDs to imitate natural light as accurately as possible. “OLEDs are a technological sensation that enables us to completely rethink artificial lighting,” enthuses Leo.

The expectations placed on OLEDs are high; they are expected to become more efficient than all existing light sources and, someday, to be able to convert nearly 100% of their energy supply into light. These weighty ambitions place demands on materials developers and lighting manufacturers alike. With electric light bulbs, halogen lamps, and energy-saving lamps, a large proportion of the energy is converted into heat instead of light – the surface of a 100-watt electric bulb, for example, reaches a temperature of more than 200C (392F) when lit. By contrast, the OLEDs being developed in Dresden remain at around 30C (86F), so they’re always safely cooler than body temperature.

The luminous efficiency of commercial OLEDs is currently between 45 and 60 lumen per watt. In the laboratory, values of more than 90 lumen per watt have already been achieved. For the purposes of comparison: A standard fluorescent tube achieves 45 to 75 lumen per watt. At 10,000 hours, the lifespan of OLEDs is also promising, even at this stage. Leo and his team are working on making these values better still. Before major lighting manufacturers incorporate OLEDs into large-scale production, they must reach a lifespan of several tens of thousands of hours and achieve an efficiency that is approximately twice that of existing fluorescent tubes.

Increasing efficacy

Luminous efficacy shows the amount of light produced per watt of electricity. It is measured in lumens per watt (lm/W).

Light for wellbeing

It is not only because of their efficiency that OLEDs are the light source of the future. “Their light is more flattering, softer and more forgiving than any other light source, which is why I call it the ‘light for wellbeing’,” says Rogier van der Heide, head designer at Philips Lighting. The secret to their ‘feel-good’ factor lies in the way they emanate light. In contrast to all other past and present artificial light sources, OLEDs do not emit light from a point; they are a flat light source. “With OLEDs, it is also possible to regulate the color temperature and adapt the light to the time of day,” explains Leo. So, it is possible to have a warm white light for the morning and evening hours and a cool white for daytime. “This is something which has hardly been seen before with lighting,” he says.

Another property of OLEDs is inspiring lighting designers as well. They are made of wafer-thin organic materials, and in the foreseeable future it may be possible to place them like a second skin over wallpaper, ceilings, or windows. This would enable a ceiling to create the perfect illusion of a summer sky, or a wall to become a virtual spring meadow. When switched off, OLEDs are white, relective, or transparent – so they could be used to help create windowpanes that let in sunlight during the day, then transform into flat lamps in the dark. The rooms of the future might be able to do away entirely with lamps as we know them today.

Carbon molecules create light

OLEDs function according to the same principles as LEDs. With both types, light is produced using semiconductors. These are solids that conduct electricity under certain conditions. When electricity flows through semiconductors, they start to glow. The difference between LEDs and OLEDs is the “o,” which stands for “organic.” While LEDs use tiny inorganic crystals based, for example, on gallium nitride, OLEDs are made from pigment-like organic compounds that are normally used to coat a base material by means of vapor deposition.

The structure of an OLED is a bit like a sandwich. The organic layers are positioned between two flat electrodes, which are around a hundred times thinner than a human hair and are invisible to the naked eye. When an electrical current is passed through them, the molecules in the organic layers start to glow. If red, green and blue substances are combined, white light is created. “We have so far used only glass as a base, but flexible materials are likely to be used in the medium term,” says Leo. The organic semiconductors must be well protected against steam and air and be properly encapsulated. It is still difficult to achieve this on pliable materials.

Well-known lighting manufacturers have already made use of the new technologies. Two of the leading companies are Osram and Philips. A few years ago, Osram, a subsidiary of Siemens, introduced the first OLED light sculpture – known as Early Future – onto the market. Since then, Osram has expanded this business and created entire conference rooms for its customers with a combination of OLED and LED lighting. In 2011, the company opened its first OLED pilot production line in Regensburg to enable such applications to be available on a larger scale in the near future. Here, Osram is researching how these sensitive light panels can be processed on an industrial scale.

The Dutch company Philips has christened its first OLED lighting module Lumiblade, presenting it in 2010 as the world’s largest OLED light installation: The wall is made up of more than 1,000 small panels. A camera records every movement made in front of it and translates them into electrical impulses that light up individual panels. The natural ‘feel-good’ light could also be used in hospitals and doctors’ surgeries in the future. Enquiries are also coming from museums interested in a gentle light source without UV rays and strong heat emission. Japan is already a step ahead; the first exhibition halls here have already been equipped with OLEDs.

The start of mass production

The new technology is inspiring Asian manufacturers in particular. In Japan, following the Fukushima nuclear disaster and the temporary closure of most nuclear power stations, almost everybody is trying to save electricity wherever possible, according to Dr. Takuya Komoda, Research Director in the organic lighting division at Panasonic. Lighting accounts for 16% of Japan’s total energy consumption. “In order to reduce the power consumption of lighting, it is urgently necessary to introduce next-generation lighting devices. OLEDs will be a very important lighting source in the future because they are able to provide both high energy savings and an excellent lighting atmosphere,” says Komoda. Although energy-saving lamps are more efficient right now, this will change. “We are planning to raise the power efficiency of OLEDs up to 100 lumen per watt by 2018.”

In 2011, the Japanese company Lumiotech, which specializes in OLEDs, gave the market new momentum by launching affordable hanging light panels and OLED desk lamps at a unit price of $410 (€315) and $650 (€500) respectively. Additionally, Konica Minolta is taking part in the lighting revolution of the future with its Symfos light panels. The company has also made headlines with a type of print head for OLEDs. Instead of ink, this device, the first of its kind, applies electronic functional materials and is thus able to ‘print’ organic lights.

Governments embrace OLEDs

Policymakers have also recognized the potential of these energy-efficient miracle lights and has been promoting their development for years. In the United States, the Department of Energy has been supporting research, development and the manufacture of efficient light sources such as LEDs and OLEDs since 2003 with its “Solid State Lighting Program”. The government’s aim is to reduce electricity consumption for lighting purposes.

In the European Union (E.U.), the aim is to achieve a 20% reduction in greenhouse gas emissions by 2020. To achieve this, the E.U. is promoting research in the energy sector, including OLEDs as an energy-saving and environmentally friendly technology of the future.

Several million euros are flowing into European research projects in which the scientific community and industry are working together to develop OLEDs that are more efficient. In Germany, the Federal Government is supporting research and development through its OLED 2015 program. Together with business partners, it has invested more than $1 billion (€800 million) since 2006. This initiative includes follow-up ventures like the Kobalt Project, launched in the spring of 2012 and involving partners such as Philips and BASF, where the focus is on developing cost-efficient OLED components for applications in the lighting market.

“Annual sales of small OLED displays already amount to around $4 billion,” says Professor Dr. Leo in Dresden. In a few years, this figure will have risen to double digits. If costs fall and efficiency increases, experts believe that nothing will stand in the way of an OLED revolution.

“LEDs have been under research for 40 years longer and thus have an edge today. But provided OLEDs reach an energy efficiency comparable to that of LEDs, both solutions will each take their own share of the lighting market – precisely because they represent complementary alternatives,” says Dr. Felix Christian Görth of BASF New Business. The organic light panels will therefore not entirely monopolize the market, even in the future. For certain applications, such as car headlights, point light sources are still in demand.

LEDs might therefore be the future of point light sources and OLEDs the future of flat lamps. For Görth it is no longer a question of whether OLED technology will be commercially successful. “OLEDs have, after all, played an important role in cell phone displays since 2011,” the BASF expert points out. “The only thing still open to debate is how big the market will ultimately be,” he adds.

The fact that the big breakthrough is still to come for OLEDs is apparent from Professor Leo’s office in Dresden. He still has a conventional reading lamp on his desk, and the room is still lit by traditional fluorescent lamps on the ceiling, yet he is convinced: “It may not be long before OLEDs become commonplace in many offices like mine.”