Hybrid White Organic Light Emitting Diodes (OLED) Processed by Organic Vapor Phase Deposition
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White Organic Light Emitting Diodes (OLED) Processed by Organic Vapor Phase Deposition M. Boesing1, F. Lindla1, C. Zimmermann1, P. van Gemmern2, D. Bertram2, D. Keiper3, N. Meyer3, M. Heuken1,3, H. Kalisch1, R. H. Jansen1 1 Chair of Electromagnetic Theory, RWTH Aachen University, Kackertstr. 15-17, 52072 Aachen, Germany 2 Philips Technologie GmbH, Philipsstr. 8, 52068 Aachen, Germany 3 AIXTRON AG, Kaiserstr. 100, 52134 Herzogenrath, Germany
ABSTRACT White OLED consisting of a fluorescent blue emissive layer combined with a phosphorescent green and a phosphorescent red emissive layer were processed by means of Organic Vapor Phase Deposition (OVPD). Different concepts to tune the color coordinates of the device are discussed with respect to the luminous efficiency. Furthermore, the influence of device aging on the emitted spectrum is being investigated by means of spectrally resolved lifetime measurements.
INTRODUCTION Organic Vapor Phase Deposition (OVPD) is a novel process for the deposition of organic thin films and was initiated by Professor Steve Forrest [1]. It offers the possibility to deposit organic layers homogeneously at a very high deposition rate [2][3] and to realize complex stack designs including for example layer cross-fading or non constant dopant concentration profiles [4][5]. These features make OVPD a promising candidate for the production of small-molecule OLED on an industrial scale. In the past, we have demonstrated an OVPD-processed red phosphorescent OLED achieving an external quantum efficiency of up to 18 % (without improved light out coupling) combined with a driving voltage as low as 3.4 V at a luminous density of 1000 cd/m2 [4]. In this work, we present an OVPD-processed 3-color hybrid white OLED. Furthermore, different concepts to tune the color coordinates of the device are being discussed with respect to the luminous efficiency of the device. In contrast to red and green phosphorescent emitting materials, today’s phosphorescent blue emitters do not exhibit a sufficient lifetime to realize a full phosphorescent white OLED with reasonable color coordinates and lifetime. The concept of hybrid white OLED combines the high luminous efficiency of red and green phosphorescent emitting materials and the long lifetime of blue fluorescent emitting materials and therefore offers the possibility to realize efficient purewhite OLED with a long lifetime. EXPERIMENT The devices to be discussed have been deposited by means of an AIXRON GEN-1 OVPD system. The concentrations of the dopants in the emissive layers are controlled by adjusting the corresponding carrier gas flow.
Figure 1 shows the layer stack of the investigated (reference) OLED. All materials (except for the electron transport material ETM002) were supplied by Merck OLED Materials GmbH. N,N'diphenyl-N,N'-bis(1-naphthylphenyl)-1,1'-biphenyl-4,4'-diamine) (NPB) is used as a hole transport material. Dicarbazolylbiphenyl (CBP) is used as a host material for the green and red phosphorescent emitting materials Ir(ppy)3 and TER0
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