OLEDs gain more and more interest in the field of lighting applications. The OLED technology provides striking advantages and covers completely new application fields offering a new freedom in design for next generation lighting. Large area OLEDs might act as a 2-dimensional light source which is thin, flat and lightweight generating diffuse, nonglaring illumination. In the first part of our report we investigate small scale inhomogeneities of polymer based OLEDs. Devices were monitored during operation by taking pictures of the active area at constant periods of time. These pictures were analyzed by a software tool with respect to the occurrence and evolution of defects. Initially induced inhomogeneities are growing and dominate the performance with increasing operation time. Within the error margin of the setup no additional spots are generated during operation. The voltage drop inside the ITO anode due to a high resistivity plays an important role for the brightness homogeneity of large area devices. The voltage drop causes a brightness fall-off towards the center of the device. It is maintaining with increasing average current density and luminance, respectively. At a brightness of 1000cd/m² the deviation at the center exceeds 30%. The homogeneity of luminance is improved by incorporation of additional metal lines on the anode layer. The best results were achieved with 200nm thick aluminum structures with a pitch of 1mm and a width of 60μm of each line. At an average current density of 45mA/cm² the decay towards the center of the device is only half of the decrease without any additional metallization.

Date Published: 20 April 2006
PDF: 9 pages
Proc. SPIE 6192, Organic Optoelectronics and Photonics II, 61920W (20 April 2006); doi: 10.1117/12.661085

Published in SPIE Proceedings Vol. 6192:
Organic Optoelectronics and Photonics II
Paul L. Heremans; Michele Muccini; Eric A. Meulenkamp, Editor(s)