Regensburg 2013 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 50: Organic semiconductors
HL 50.10: Vortrag
Mittwoch, 13. März 2013, 12:00–12:15, H13
Self-passivation of molecular n-type doping during air-exposure using a highly efficient air-instable dopant — •Max Tietze, Florian Wölzel, Torben Menke, Axel Fischer, Björn Lüssem, and Karl Leo — Institut für Angewandte Photophysik, TU Dresden
Since several process steps of organic field effect transistors like photo-lithography cannot be performed in vacuum or inert atmosphere, an application of n-doping with the most efficient molecular n-type dopants is hampered because they are prone to be air-instable due to their low ionization potentials. We study systematically the degradation of films of the n-dopant tetrakis(1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidinato)ditungsten(II) (W2(hpp)4) on different substrates and doped into C60 films by conductivity measurements, photoelectron spectroscopy, and laser desorption/ionization time of flight mass spectrometry. We find that the conductivity of n-doped C60 layers is restored after air-exposure, if annealed in vacuum. Hereby, the majority of the dopant molecules decompose immediately after air-exposure, whereas the remaining W2(hpp)4 molecules stay intact and slowly degrade with an exponential decay time of ≈11 min. These findings are explained by passivation of W2(hpp)4 molecules, which are in a charge-transfer state and thus protected from further oxidation. Hence, the conservation of the conductivity can be understood in terms of a self-passivation of molecular n-doping and an application of highly efficient n-doped thin films in functional organic devices processed even under ambient conditions is feasible.