OLEDs (Organic Light-Emitting Diodes) consist of a multilayer structure of organic materials between two electrodes: Sandwiched between several charge transporting layers, the central layer (emissive layer), guarantees the light emission: Modern OLED displays consist of red, green and blue (RGB) pixels arranged side-by-side. As these pixels are self-illuminating, they do not require a backlight unit like the LED technology. Therefore, OLED displays have a much simpler structure, resulting in thinner display panels. In contrast to the widespread LED technology, OLED displays have many further advantages: they feature low power consumption, a high contrast and a high resolution. Of particular interest is the use of OLED displays on transparent and flexible surfaces, which enable completely new product designs.
OLED technology can also be used for lighting applications. Thanks to the OLED technology, these luminous panels can emit a pleasant, two-dimensional, homogeneous light. In addition, they can be transparent or flexible, and allow new possibilities of integrating illuminating material into architecture or lamps due to their reduced volume and weight. This makes it possible not only to design lighting products in a completely new way, but to create new lighting concepts for the design of interior or exterior facades. The possibilities with flexible devices of various forms represent a disruptive technology to the general lighting market value chain.
The heart of the OLEDs are the so-called emitters. They convert electrical energy into visible light, which leads to the perception of red, green or blue pixels. To date, three different technological concepts can be used to generate light: fluorescence, phosphorescence and thermally activated delayed fluorescence (TADF). The main differences between these concepts are explainable through quantum mechanics. In an OLED, the electrical current leads to an excitation of the molecules and thereby to the creation of singlet and triplet excitons. The energies of the singlet exciton are higher than those of the triplet excitons, but for every singlet exciton three triplet excitons are generated. The first generation of emitters, the fluorescent emitters could only convert the singlet excitons and therefore only 25% of all excitons into light. Phosphorescent and TADF emitters, on the other hand, can convert up to 100 percent of the excitation energy into light by using both, the singlet and the triplet excited states.