Berlin 2001 – scientific programme
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CPP: Chemische Physik und Polymerphysik
CPP 17: Poster: Spectroscopy and Single Particle Spectroscopy of Molecular Systems, Photoprocesses, Biological Systems
CPP 17.7: Poster
Tuesday, April 3, 2001, 12:30–15:00, AT1
Valence band structure and localised states in starburst trisphenylquinoxaline — •Maria Benedetta Casu1, Paolo Imperia1, Sigurd Schrader1, Markus Jandke2, and Peter Strohriegl2 — 1University of Potsdam, Institute of Physik, Am Neuen Palais 10, D-14469 Potsdam, Germany — 2Makromoleculare Chemie I, University of Bayreuth, D-95440 Bayreuth, Germany
In this work we studied a starburst trisphenylquinoxaline by means of Ultraviolet Photoelectron Spectroscopy (UPS) and Thermally Stimulated Luminescence (TSL). UPS provided not only the characterisation of the valence band structure but also parameters like ionisation potential, 6 eV, and, combined with optical spectroscopy, electron affinity, 2.8 eV, that are important in combining better OLEDs configurations. Knowing that, we localised the energetic position of valence and conduction band of the investigated substance. On the other hand, a wide distribution of localised states occurs in organic layers due to several factors like impurities or structural defects; TSL can investigate these states. The combination of the used techniques together with semi-empirical quantum chemical calculation, gave a detailed description not only of the valence and conduction band of the studied materials, i.e. the energy position of HOMO (highest occupied molecular orbital ) and LUMO (lowest unoccupied molecular orbital), but also of the trap distributions localised in the band gap: a shallow one at 0.06 eV and a deeper state centred at 0.24 eV. The full spectroscopic and electrical characterisation of the material formed the background for understanding its behaviour in heterolayer devices