www.afm-journal.de FULL PAPER wileyonlinelibrary.com © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Adv. Funct. Mater. 2010, XX, 1–10 1 www.MaterialsViews.com By Ozlem Usluer,* Serafettin Demic,* Daniel A. M. Egbe, Eckhard Birckner, Cem Tozlu, Almantas Pivrikas, Alberto Montaigne Ramil, and Niyazi Serdar Sariciftci 1. Introduction Since the electroluminescence from small molecular organic materials was reported for the first time in 1987 by Tang and VanSlyke, organic light-emitting diodes (OLEDs) have attracted much attention and found their way into markets as displays. [1] With their advantages of low-power consumption, high contrast and high brightness, they have applica- tions in full color flat panel displays. [2,3] The general structure of OLEDs con- sists of a light emissive layer sandwiched in between two metal electrodes, one of which is transparent conducting electrode ( Figure 1). Additional layers between the cathode and the emissive layer (elec- tron transport layer, ETL) or between the anode and the emissive layer (hole trans- port layer, HTL) is used for high efficiency OLED devices. Recent studies revealed that organic multilayer structures typically enhance the performance of the devices by lowering the barrier for hole injection from the anode and by enabling control over the electron-hole recom- bination region, moving it from the organic/cathode interface, where the defect density is high, into the bulk. Hence, the layer deposited on the anode would generally be a good hole transport material (HTM), providing HTL. Similarly, the organic layer in contact with the cathode would be the optimized ETL. [4] In general, high glass transition temperature ( T g ) amorphous hole transport materials (AHTMs) are needed to have an effi- cient and stable OLED device. The most widely used HTLs, N,N′-bis(3-methylphenyl)- N,N′-diphenylbenzidine (TPD) and 4,4 ′-bis[ N-(1-naphthyl)- N-phenyl-amino]biphenyl (NPB), offer many attractive properties such as high charge carrier mobility and ease of sublimation. They possess some disadvantages to be used in long-lifetime OLED devices such as their rather low T g Fluorene-Carbazole Dendrimers: Synthesis, Thermal, Photophysical and Electroluminescent Device Properties Novel hole-transporting dendrimeric molecules containing dioctylfluorene, spirobi(fluorene) and spiro(cylododecane-fluorene) as the core unit and dif- ferent numbers of carbazole and thiophene moieties as the peripheral groups are synthesized. All the dendrimers are characterized by 1 H NMR, 13 C NMR, FTIR, UV–vis, PL spectroscopy, and MALDI-TOF. They are thermally stable with high glass transition and decomposition temperatures and exhibit chemically reversible redox processes. They are used as the hole-transporting layer (HTL) material for multilayer organic light emitting diodes (OLEDs) with a low turn-on voltage of around 2.5 V and a bright green emission with a maximum luminance of around 25400 cd m -2 . DOI: 10.1002/adfm.201001153 [∗] Dr. O. Usluer, Dr. S. Demic Solar Energy Institute Ege University, 35100, Bornova, Izmir (Turkey) E-mail: ozlem.usluer@ege.edu.tr; serafettin.demic@ege.edu.tr Dr. D. A. M. Egbe, Dr. A. Pivrikas, Dr. A. M. Ramil, Prof. N. S. Sariciftci Linz Institute for Organic Solar Cells (LIOS) Physical Chemistry Johannes Kepler University Altenbergerstr. 69, A-4040 Linz (Austria) Dr. E. Birckner Institute of Physical Chemistry Friedrich Schiller-University Jena Lessingstrasse 10, 07743 Jena (Germany) Dr. O. Usluer Department of Chemistry Art and Science Faculty Mugla University 48000, Mugla (Turkey) C. Tozlu Department of Physics Art and Science Faculty Mugla University 48000-Mugla (Turkey) Figure 1. General structure of OLED device.