OLED is shorthand for organic light-emitting diode. Here, the attribute "organic" refers to materials from organic chemistry that are utilised in OLED.

The diodes consist of several different layers of materials – each of them has to fulfil a specific task: starting with the carrier material, nowadays most of the time glass, in select cases also metal, all the way to the encapsulating cover glass, ten different layers are nothing unusual.

Among them are, in part, transparent electrode materials, electron-transporting materials, and the actual organic emitter materials in which light is generated. The individual materials are applied in very thin layers – some a few nanometres thin – in large areas on the carrier substrate (for instance pre-treated sheets of glass). This way, an evenly luminescent series of layers is created in which each individual emitter layer can luminescence.

For the manufacturing, either small molecules or polymer materials are utilised. At present, small molecules are being used predominantly. In comparison to polymer materials, small molecule OLEDs last longer and are more efficient. OLEDs generate light  in the visible range exclusively.

Depending on the combination of the individual layers, they emit monochrome light, i.e., light of a single colour, or white light that consists of several light colours. In this, warm-white and cold-white colour tones are possible. The light emitted is radiated by the OLEDs diffuse, homogenous, and almost Lambertian, meaning it is radiated evenly in all directions, in a single direction (in case of intransparent OLEDs) or in two directions (in case of transparent OLEDs).

Flexible and user-friendly

The design potential offered by OLEDs is first and foremost due to the appearance that is rich in facets – even when switched off - through which completely new applications open up, especially to designers: If an OLED is, for example, designed as a reflective surface, it generates the effect of a luminescent mirror when switched on.

OLEDs can also be completely transparent – the light then appears almost "out of nowhere". However, at present, the most common type of construction is the OLED as a matt-white sheet.

Integrated in mirrors, windows, or other sheets of glass, in furniture made of wood or metal, as well as in luminaires, OLEDs offer the opportunity to experience light from unusual, new perspectives.

Because: With their diffuse light distribution, OLEDs can support well-being through a pleasant, continuous light spectrum. The effect of light on people is one of the focal points of the research in illumination technology. In this, one focus is on aligning this effect with the needs of different user groups, in which the OLED can be superior to the LED in a lot of applications.

Developments and trends

The developments in the area of OLED technology are currently coming along very promisingly. Many large manufacturers such as Philips, Osram or Panasonic have already recognised its potential and invested into first production plants. But smaller companies have set up first pilot lines, too.

By now, a square design of approx. 15 cm x 15 cm has become dominant as the maximum dimensions of OLEDs. At present, this is due to the efficiency and cost limits of the material of the transparent anode.  For this reason, the OLED will also in the future not exceed a format of 30 x 30 cm. Another factor is the optimal utilisation of the available glass surface provided by this form. Nevertheless, some manufacturers have made it their objective to realise any shape imaginable – depending on the customer's wish.

The manufacturers have identified the market of general illumination as the target market with the highest potential and are developing the characteristics of the OLED targetedly in this direction. Of the utmost importance, here, is efficiency, i.e., the relation of the energy utilised vs. the light generated.

While up to 160 lm/W are already being achieved in case of the LED, the current efficiency of the OLED is between 30 lm/W and 60 lm/W. Another focus is at present being directed at the luminous flux, where some panels already exceed the 100 lm, while a further increase is being worked on. In particular, the colour rendering index – meaning the ability of a light source to reproduce colours naturally – is also naturally very good in case of OLEDs.

To overcome the currently steepest hurdle on the path to market acceptance, the high price, manufacturers in the entire illumination industry are looking for buyers that have a very high demand for OLEDs. However, luminaire manufacturers, private individuals and luxury outfitters are currently still looking for suitable applications in which the OLED can play out its advantages to the fullest.

Due to this "chicken vs. egg" problem, the trends for OLED applications are, at present, heading in very different directions. Automotive manufacturers are experimenting with OLEDs in rear spotlights, designers are creating OLED light art objects, luminaire manufacturers count on free-standing luminaires or suspension luminaires and combine LEDs with OLEDs.

Opportunities for municipalities

First areas of utilisation for OLEDs in the urban landscape could be the facades of buildings into which the means of lighting is integrated. Sidewalks with recess-mounted OLEDs would also be imaginable. In public buildings, the organic light-emitting diode could be utilised in general lighting. For museums, the OLED is ideal, too: Due to the lower amount of heat generated and due to the good colour reproduction, it can be utilised everywhere where sensitive materials need to be illuminated.

Interesting to municipalities may also be the interaction of illumination and information presentation, for instance at bus stops. Driven by the very positive development of the OLED displays, the prices of materials are dropping. A combination of light and display functions as such provides for new perspectives in municipal planning.