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20 April 2006Polymer light-emitting devices for large-area lighting
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.
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C. Gärditz, R. Pätzold, D. Buchhauser, J. Wecker, A. Winnacker, "Polymer light-emitting devices for large-area lighting," Proc. SPIE 6192, Organic Optoelectronics and Photonics II, 61920W (20 April 2006); https://doi.org/10.1117/12.661085