Influence of deposition chamber pressure and substrate temperature on the properties of fluorescent blue and phosphoresc
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1003-O03-24
Influence of deposition chamber pressure and substrate temperature on the properties of fluorescent blue and phosphorescent red OLED deposited by OVPD Philipp van Gemmern1, Christoph Zimmermann1, Phenwisa Niyamakom2, Matthias Wuttig2, Sabine Brand3, Holger Schwab3, Heinrich Becker4, Rocco Fortte4, Michael Heuken1,5, Holger Kalisch1, and Rolf H. Jansen1 1 Institut f¸r Theoretische Elektrotechnik, RWTH Aachen, Aachen, 52056, Germany 2 Institute of Physics (IA), RWTH Aachen, Aachen, 52056, Germany 3 Philips Technologie GmbH, Philipsstr. 8, Aachen, 52068, Germany 4 Merck OLED Materials GmbH, Frankfurt/Main, 65926, Germany 5 AIXTRON AG, Kackertstr. 15-17, Aachen, 52072, Germany
ABSTRACT Organic light-emitting diodes (OLED) offer the potential to replace conventional light sources such as incandescent bulbs and fluorescent tubes. The question which thin-film technology is most favorable to produce OLED on an industrial scale is still unanswered. The most established technology for the deposition of small-molecule organic layers is vacuum thermal evaporation. A comparably novel technology is organic vapor phase deposition (OVPD), which offers some unique features in terms of adjustable process parameters such as deposition chamber pressure (P) and substrate temperature (TS). The impact of these parameters on the morphology of organic single layers as well as on the performance of OLED is mostly unknown. In this work, phosphorescent red OLED were produced with different TS and a strong influence on the device efficiency was found. Atomic force microscopy measurements were conducted to investigate the morphology of the hole injection and hole transport layers of the devices deposited at different TS. In addition to this, the influence of TS and P on the performance of fluorescent blue OLED and the morphology of organic single layers was tested. By varying TS and P for the emission layer only, current efficiencies in the range from 4.3 to 6.8 cd/A were found despite the fact that all devices had the same structure. Atomic force microscopy measurements conducted on organic single layers which were deposited at the same process conditions showed rms values ranging from 1.4 to 57 nm.
INTRODUCTION Promising candidates for replacing conventional light bulbs are light-emitting diodes (LED) as well as organic light-emitting diodes (OLED), whereby the latter offer some unique features which make them more suitable for general lighting. OLED are thin, diffusive light sources which offer a high grade of flexibility in terms of design and employment. Nevertheless, OLED are a comparably young technology and until today, there are hardly any OLED lighting products on the market. While scientists all over the world work on improving the efficiency and lifetime of OLED and new records are published in short intervals, the question regarding the most suitable technology for the fabrication of OLED on an industrial scale is still unanswered.
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