Berlin 2008 – scientific programme

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SYSA: Symposium Tayloring Organic Interfaces: Molecular Structures and Applications

SYSA 5: Poster Session SYSA

SYSA 5.62: Poster

Tuesday, February 26, 2008, 14:30–20:00, Poster A

Improved efficiency of phosphorescent organic light emitting devices at high brightness — •Sebastian Reineke, Gregor Schwartz, Karsten Walzer, and Karl Leo — Institut für Angewandte Photophysik, 01062 Dresden, Germany

We present a novel emission layer (EML) structure for phosphorescent organic light emitting diodes (OLEDs) comprising mixed films of fac tris(2-phenylpyridine) iridium [Ir(ppy)₃] dispersed in 4,4’,4”-tris(N-carbazolyl)-triphenylamine (TCTA) which reduces the decrease of efficiency at high current densities. Based on results of photoluminescence experiments, we intermit the EML with thin neat layers of TCTA. Due to its high triplet energy, TCTA acts as an exciton blocking layer inside the EML which suppresses exciton migration on the dopant sites and, consequently, triplet-triplet annihilation. We show that this EML structure leads to a smaller efficiency decrease: Starting at initial external quantum efficiencies (IEQE) of 15.8 % and 14.4 % at low brightness for the reference and interlayer device, respectively, those structures yield critical current densities j_c of 140 mA/cm² and 270 mA/cm². Here, j_c defines the current density where the IEQE drops to half of its value.