Logo of the Physikalisch-Technische Bundesanstalt
symbolic picture: "magazines"

How long can OLEDs glow?

Especially interesting for
  • manufacturers of OLEDs

Organic light-emitting diodes (OLEDs) are novel, large-scale light sources which are based on organic semi-conductors and have been commercially available for approx. 2 years. The particular properties of OLEDs require new measurement procedures to determine their service life. Within the scope of an extensive study, PTB has, in collaboration with all European OLED manufacturers, determined criteria that are relevant for the service life of OLEDs.

The new measuring facility allows numerous different measurands to be determined.

OLEDs consist of large-scale layers of organic materials – which are, however, only a few hundreds of nanometres thick – in which the light is generated. In the course of their operation, the organic layers wear out, and undesired effects may occur, such as, e. g., a change in the light colour. A clearly visible change in the light colour and decreasing brightness are both phenomena which are, by far, not desired by many consumers, so that these two criteria can be considered relevant for the estimation of the service life of an OLED.

Within the scope of a cooperation project, PTB has developed a measuring facility to assess the service life of OLEDs and used it to investigate 60 OLEDs manufactured by the companies Osram OS and Philips, as well as by the Fraunhofer Research Institution COMEDD. The measuring facility allows all optical, thermal and electrical measurands which are relevant for OLEDs to be monitored insitu. Specifically, the mean and spatially resolved luminance, the spectral composition of the light, and, thus, its correlated colour temperature and colour rendering for various viewing angles as well as the OLED supply voltage, operating current and temperature are recorded.

The service life of OLEDs amounts to several thousands of hours and is determined in practice by means of so-called "accelerated ageing procedures". Within the scope of the project, the new measuring facility was also used to validate accelerated ageing tests. Hereby, the project partners operated identical OLEDs, for example, at clearly elevated currents, so that their service life ended after only a few hundreds of hours of operation. A model for the determination of the service life under real-life conditions was developed and then validated.

Based on these results, a standardized measurement recommendation for OLEDs is now being elaborated in a Technical Committee at the International Commission on Illumination (CIE) under the leadership of PTB. Furthermore, a detailed description of the methods for the determination of the service life of OLEDs presented here will soon be published in the form of a book.

Scientific publication

Gerloff, T.; Sperling, A.; Lindner, D.; Meyer, M.; Pends, S.: In situ measurements of OLED lifetime. Proc. NEWRAD 86 (2011)