Regensburg 2013 – scientific programme

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DS: Fachverband Dünne Schichten

DS 31: Organic thin films II

DS 31.2: Talk

Thursday, March 14, 2013, 15:00–15:15, H8

In situ Spectroscopic Ellipsometry Monitoring of Alq₃ and α-NPD Alkali Metal Doping — •Francisc Haidu¹, Ovidiu D. Gordan¹, Christoph Werner², Maciej Neumann², Norbert Esser², and Dietrich R. T. Zahn¹ — ¹TU Chemnitz, 09126 Chemnitz, Germany — ²ISAS Berlin, 12489 Berlin, Germany

The electron- and hole-transport organic materials Tris-(8-hydroxyquinoline)-aluminium(III) (Alq₃) and N,N’-Di-[(1-naphthyl)-N,N’-diphenyl]-(1,1’-biphenyl)-4,4’-diamine (α-NPD), respectively, were investigated in their pristine and reduced form via alkali metal (AM) doping. The two organic molecules are seen as milestones in organic light emitting diode functionality, and moreover AM doped molecules show interesting magnetic, electric, and physical properties. Extensive photoemission, inverse photoemission, vibrational spectroscopy, and theoretical studies of n-doped Alq₃ and α-NPD were performed in the last decade. The optical properties of pristine materials were previously established via spectroscopic ellipsometry (SE). This work is the first SE analysis of the doping process. In situ SE studies in the (0.7-5.0) eV energy range were performed by a lab-based SE and extended up to 9.5 eV by a vacuum ultraviolet ellipsometer at the synchrotron facility BESSY II, Berlin. The determined optical band gaps show evolution in agreement with filling and splitting of the lowest unoccupied molecular orbital due to AM electron donation [1, 2]. [1] M. Knupfer, H. Peisert, and T. Schwieger, Phys. Rev. B 65 (2001) 033204; [2] T. Schwieger, M. Knupfer, W. Gao, and A. Kahn, Appl. Phys. Lett 83 (2003) 500.