OLEDs (Organic Light-Emitting Diodes) are ultrathin self-emissive devices consisting of a multilayer structure of organic materials between two electrodes: Sandwiched between several charge transporting layers, the central emissive layer makes for the light emission. OLED displays consist of the three colors red, green and blue. Being self-emissive, they do not require a backlight unit as it is needed for the LCD technology. Therefore, OLED displays have a much simpler structure, resulting in thinner display panels. In addition, OLED displays have many further advantages: they feature low power consumption, a high contrast ratio and a high resolution. Of particular interest is the use of OLED displays on transparent and flexible surfaces, which enable completely new applications and product designs.
OLED technology can also be used for lighting applications, providing a pleasant, two-dimensional, homogeneous light. In addition, they can be transparent or flexible, thus allowing for new possibilities of integrating illuminating units into architecture or lamps due to their reduced volume and weight. It is thus possible to not only design lighting products in a completely new way, but to create new lighting concepts for the design of interior or exterior facades. The creation of flexible devices of various forms represents a disruptive technology to the general lighting market value chain.
The heart of the OLEDs are the emitter materials. These are organic molecules that are able to convert electrical energy into visible light. Depending on their structure, the three colors red, green or blue are generated. 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 their different energy efficiency, which can be explained by quantum mechanics: In an OLED, the electric current leads to an excitation of the emitter molecules and thereby to the creation of singlet and triplet excitons. Due to quantum statistics, 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. Second and third generation emitters, 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.